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    yellow colorized etching of rings of angels

    Astronomy According to Dante

    Plough interviews astronomer Sperello di Serego Alighieri.

    By Sperello di Serego Alighieri

    May 19, 2021
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    • C Jay

      Beautiful Splendid Artistic Written Works!

    • Michael Kozubek

      Great interview with Dante's descendant. Wonderful history of early science and its connection with religion.

    Even apart from these, men could fall at a single breath when pursued by justice and scattered by the breath of thy power. But thou hast ordered all things by measure and number and weight.
    (Ecclus. 11:20)

    This year, on the feast of the Annunciation, Pope Francis issued the Apostolic Letter, Candor Lucis Aeternae, marking the seven hundredth anniversary of the death of Dante Alighieri. The Pope wrote, “I wish to join my predecessors who honoured and extolled the poet Dante … and to propose him anew for the consideration of the church, the great body of the faithful, literary scholars, theologians and artists.”


    Plough: Sperello, I’m so pleased we were able to arrange this talk. Why don’t we start out here: What is your usual work, and how did you become involved with your ancestor’s work?

    Alighieri: Of course in our family we are well aware of the descendance. When I was a kid, around six years old and learning to read, my father gave me a little paper bookmark – you know, a nice one, painted – and it had on it some of the few verses of Dante which I know by heart. I’ll say them in Italian and then I’ll translate them:

    O poca nostra nobiltà di sangue …
    Ben se’ tu manto che tosto raccorce:
    sì che, se non s’appon di dì in die,
    lo tempo va dintorno con le force.

    And that means something like

    O you little nobility of our blood,
    You are just like a mantle that soon shortens:
    If you do not add to it from day to day
    Time goes around with its scissors. …

    This was the teaching from my parents – how should I deal with this nobility, this descent? And they taught me with Dante’s poetry: you can’t sit on it, you have to do a job.

    You have to maintain it, or cultivate it – to make yourself worthy.

    Yes. And later, in high school, I did study Dante, like everyone else at the time: in Italy, we read the Inferno, the Purgatorio, and the Paradiso, one each year, in the last three years of high school. I went to a classical high school; we studied Greek, Latin, Italian, philosophy, and also math and physics. I liked Greek very much, but my passion of course was for math and physics. The Italian teacher said, “You should study your ancestor better.” Well, I didn’t really like that I had to do something just because I was a descendant. Our scores in school go from zero to ten; at some point, I told her, for Italian, a six is enough for me, it’s sufficient. She took my word on it, stopped bothering me to study Dante, and always gave me a six.

    In University I did physics in Pisa, then moved to Padua, and got my Laurea – it’s not exactly a PhD; we didn’t then have PhDs in Italy – and became a doctor in astronomy. And I had a whole career in astronomy, and didn’t care much about Dante. It was only ten years ago or so that I got interested in astronomy in Dante’s work.

    I also thought, finally, well, since I am a descendent I had better do something about it. So I read a lot of books and I spoke at conferences, and then last year I got a proposal from a famous Dante expert; he is also the president of the Società Dantesca in Florence, of which I am a member. And he said that La Repubblica, one of the major Italian newspapers, had commissioned him to do a series of books for this Dantean year, and asked whether I would be willing to do the one on astronomy and cosmography. I accepted, and found a co-writer, another astronomer, and the book came out on April 23. We’re preparing an English version as well.

    Can you describe Dante’s world-picture, his cosmography, and its origins?

    red colorized etching of two figures on a cliff edge looking into Hell illustrating Dantes work

    Gustave Doré, The Vision of Hell (Inferno), colorized Image public domain

    Dante’s astronomy was inherited from the Romans and before them, the Greeks. This was the view of Ptolemy: the earth is at the center of the universe and planets and the Sun go around it in circular orbits. Everything is circular. The moon circles around the earth, and then there are the five planets visible to the ancients: Venus, Mercury, Mars, Jupiter, and Saturn. And then beyond them you have the fixed stars, and beyond that, the empyrean, where God lives.

    And the Divine Comedy is the story of travel across this universe. It starts from the surface of the earth, then goes down through hell, to the center of the earth, which is of course also the center of the universe. That is the Inferno, the first book: Dante goes to the center of the earth, which is also the point where gravity is focused; of course he understood that the earth is a sphere. When Dante and Virgil get to the center of the earth, they travel along the body of the devil, himself trapped in that center, and at the middle of the body, gravity flips. They were going down; then, when they reached the midpoint of the devil’s body, they began to go up, towards the surface of the earth on the opposite side, and eventually they emerge directly opposite from where they had started, at Mount Purgatory, which is on the opposite side of the earth. And then, in the Purgatorio, they go up this mountain, and arrive at the top.

    This whole trip Dante has done with Virgil, but since Virgil was not baptized, he can’t bring him further. So Beatrice takes over from Virgil, and they travel above into Paradise: first to the moon, then to all the planets, then to the fixed stars and the empyrean. It is a story, in a way, of space travel, one of the first works of science fiction.

    I can remember being very surprised when I realized that in the medieval world-picture the center of the universe was actually the worst place. That sort of flipped my mind around.

    So how has immersing yourself in this other world-picture influenced your own astronomy work – or has it? Because we’ve inherited a world picture that isn’t just different in shape, but is different in meaning. Dante’s Cosmos was not alive in the sense that an animist would think of a living Cosmos, but it wasn’t dead either: it was an expression of God’s wisdom. Often when people today speak of natural law, they don’t mean it in that way, but they mean it in a more mechanical way, a Newtonian way. Can you see a way to a fusion between our contemporary way of seeing the universe and a sense of the universe as a Cosmos, as an ordered and beautiful whole?

    In Ptolemy’s view, there was no hell, there was no Mount Purgatory, it was just that the earth was at the center of the universe. But Dante’s way was completely linked to God. The story goes that when Lucifer, who was originally an angel, was chased from paradise by [the archangel] Michael, he was thrown to the earth. And the force of his hitting earth created hell as a kind of crater, and the mountain of purgatory was the displaced earth pushed out the other side. So God created the shape of the world for specific reasons, which are very much linked to our redemption.

    Later on, of course, the view changed, saying that the sun is at the center, and all the planets rotate around it; that the moon rotates around the earth but other planets also have moons – Galileo found the moons around Jupiter and so on. And then we were pushed even further out of the center: in the eighteenth century, William Herschel thought that the sun was more or less in the center of our galaxy, which is not true. But it’s not just that we are not at the center of our universe, and in fact there is no center, but also that the universe couldn’t care less about us. That is the contemporary view. The universe exists very much independently of us; maybe there are others out there, other living beings. So we were pushed out of the center not just physically, but in terms of importance: the universe existed by itself much earlier than we were there, and will probably last much longer than we do. So this is really a change of paradigm, if you like.

    I’m a Christian, and I suppose I see the world through a kind of double overlay, because obviously the universe as we know it through contemporary astronomy doesn’t look like Dante’s cosmos. But it does, to me at least, look like a cosmos; it has the character of creation.

    Well, yes, and I was brought up in a Catholic family, I was educated like that, but it seems to me that we should not mix things. Our approach to science must be opening our eyes and believing only in what we see and demonstrate. And science is a route of errors: you improve by mistakes, it is cautious and tentative. And of course in religion the approach is completely different: you have to abandon yourself, to have faith, to trust, to believe in something you don’t necessarily see. So one should not use the same approach to both. It would be misleading to try to do so. But that does not mean that one person cannot have both approaches, applied to the appropriate areas.

    Let me try to make an example. If you eat pasta, you have to put it in your mouth and chew it with your teeth, and then you can swallow it. If you drink wine, then it’s different: you just sip it and it goes down. And you can’t mix up the two: you cannot chew wine and you cannot sip pasta. But the same person can eat pasta and drink wine, no problem. But he has to use different methods.

    For a scientist, it is not easy. I have had periods in my life when I thought, no, no, the only approach is the scientific one, I cannot have another one, for me it is impossible. But then later, I realized that this is not true – you can have both. Just don’t mix them.

    I don’t think that it is possible for science to say that God does not exist. 

    I agree, but at the same time – I feel like I’m always wanting to mix them, I want to be able to see the universe as a cosmos.

    Well, you can do that, in a way, and it is maybe easier in the contemporary scientific picture. For example, we scientists know that the universe has had a beginning, what we call the Big Bang, and we know how far in the past it is: it’s not what the Bible says, but that doesn’t matter, because the Bible doesn’t necessarily say the time span, that’s not its purpose. But we know it is thirteen and a half billion years ago. It does have a beginning. And you can view that as the creation: there is no difference. We don’t know, and will never know – it’s impossible to know what was before that.

    In principle you can’t look beyond it.

    Yes. It looks like a creation. Many scientists do not call it a creation, because they don’t believe, but you can view it as one, no problem. There are points of contact, but the approach still has to be different.

    I agree. Half the time it seems to me that things like string theory are attempts to get around the implications of the universe’s having a beginning, because string theorists don’t want it to.

    The thing with those kinds of theories – you can call them theories, but it’s more speculative philosophy than science.

    Because it is in principle untestable.

    Yeah, it is not testable. It’s the same thing as multiverse theory, maybe there are many universes, OK, we can talk about it, but so what? It’s not testable. But even then, in a multiverse scenario, it is entirely possible to ask whether someone can have created all these universes. I don’t think that it is possible for science to say that God does not exist. But also the other way: religion should not close down inquiry into how the universe developed; this is up to scientists.

    You live very close to where Galileo lived, yes?

    Now I am in Perugia, but when I was working at the Arcetri Observatory in Florence, that was right near the house where Galileo lived the last nine years of his life, when he was put in confinement by the church. I went there many many times; at the Observatory we had the keys to the place.

    Maybe an example of how not to do the interaction of science and religion.

    Well, in a sense, but also not: Galileo was a Catholic man, no doubt about that; he made some discoveries, because he used his telescope for the first time to look at the sky. He had no problem with his own discoveries, they were in no way challenging to his faith. It was a problem for the church to accept his discoveries, because the church has not always been so open.

    But you know, it’s a more complicated story: Galileo pointed his telescope at the sky for the first time in 1609, and he immediately made a lot of discoveries; this new instrument opened up so much. He discovered the mountains on the moon, and the five satellites of Jupiter; the phases of Venus; he realized the Milky Way was a galaxy, made up of stars; and he published this in 1610, the Sidereus Nuncius, the Starry Messenger.

    And immediately he became very famous because of these discoveries, and then the year after, he was invited to go to Rome. There he met Christopher Clavius, a Jesuit, who had led the team to reform the calendar in 1582. This was twenty-eight years or so later; [Clavius] was an old man. In the beginning, he did not believe Galileo’s discoveries, but Galileo had brought his telescope, and Clavius looked through, Galileo showed him, and he was convinced.

    And so [Galileo’s] discoveries were accepted by the Jesuits; Cardinal [Robert] Bellarmine asked the mathematicians of the Collegio Romano to certify his discoveries, and they did. At that time, he met Federico Cesi, who had just founded the Accademia de Lincei; Galileo became the sixth member of that academy.

    So he was well-accepted in Rome. It was only after that that things got complicated. Then as now, there were many factions in the church, some quite open, some not. And eventually he had a run-in with the not-so-open ones, and they had the trial and put him under house arrest. It was bad, but it wasn’t too bad – Giordano Bruno was killed. But Galileo could continue his work, he continued to see pupils and write books. And immediately there were large parts of the church which were quite convinced, even before the church as a whole accepted these discoveries. And it was the Jesuits who were the most open to him.

    To explain a little more about this complicated picture, I’ve got to tell you that I’m very interested in China …

    For Dante, astronomy was a kind of contemplative art.

    You sent me that piece you wrote on driving the silk road, from Perugia to Beijing.

    Yes, I became interested because of that trip, which was in 2006. And I became interested in a story which is very much connected to Galileo: the reform of the Chinese calendar, which happened in the first half of the 17th century.

    This is Matteo Ricci!

    Yes, Matteo Ricci was involved; he got to China in 1582, the same year as the reform of the Gregorian calendar. And the Jesuits wanted to get into China for the purposes of evangelization, of course; it was very difficult to get in. Francis Xavier had tried some years before, but he could only get as far as Shangchuan Island, to the south of the mainland. But Matteo Ricci was able to get into China, and eventually to Beijing, and the way he could do that is because at that time the Chinese had a serious problem with their calendar.

    The Chinese calendar is both a solar and lunar calendar. It’s very old, from the third millennium before Christ. And at that time, they had lost the rules for keeping it in phase with astronomical phenomena. This was a real problem, because in China, the emperor is the Celestial Emperor, he comes from the sky, and he has to show the people that he understands the sky; that there is a relationship between Heaven and the emperor.

    So this astronomical problem was becoming a political problem, and the emperor knew he needed an astronomical solution. Matteo Ricci was a Jesuit, educated at the Collegio Romano in Rome, where Clavius was teaching, and so Ricci had some astronomy in his education. Not much, but enough to get him to Beijing; the Chinese knew he was coming from the West with this new astronomy. They were convinced that he could help them solve the problem of the calendar.

    It was very funny – Ricci’s letters back to Rome were basically telling them about this problem and saying “Send a real astronomer!” Eventually, what happened was this: Before making his discoveries, before going to Rome, Galileo had taught in Padua, and one of his students was a German, Johannes Schreck, who called himself Terrentius in Latin. And Terrentius was in Rome, and attended when Galileo presented his discoveries to Clavius and Cesi; he was a really good astronomer; he’d had Galileo as a teacher! He actually became the seventh member of the Accademia dei Lincei, right after Galileo.

    But he was young, and he wanted to travel, to go make his own discoveries. At that time the only way you could do that was to become a Jesuit. Then you could go and travel. So that is what he did, but that meant he had to give up his membership in the Accademia. And he traveled to China, in 1618, because Ricci had been writing letters back to Rome asking that they send a proper astronomer.

    So Terrentius got to Beijing and he helped with solving the problems with the calendar. This was a big deal: up to a hundred men manned what was called the Office of Astronomy in Beijing. The Jesuits got right into it, and eventually the Emperor made them the heads of it. It was an amazing place: of course there were the Chinese astronomers, who were working in this ancient, ancient tradition, more than 4000 years old, but there were also some Muslim astronomers, who had gotten in before Ricci; the Muslim empires had expanded, and the Chinese empire was not so closed that they wouldn’t let them in.

    So there were the Chinese astronomers, the Muslim astronomers, and the Jesuits. And the turning point of the competition between them was a solar eclipse in Beijing, which happened on June 21, 1629. The story says that the emperor asked these three sets of astronomers to make a forecast of the eclipse and write it down. So they all made their forecast, and the Jesuits got it right. The Muslims got it completely wrong, and the Jesuits got it substantially better than the Chinese. So on the first of September, the following year, the Emperor officially gave the Jesuits the charge of reforming the calendar.

    The Jesuit astronomers were not alone. They had Chinese pupils working with them. One in particular, Xu Guangqi, was a pupil of Ricci, and a Catholic convert. He was a very important person, a high-ranking functionary in the Empire. The Emperor gave to Xu Guangqi the task of reforming the calendar. He became the head of the office for astronomy, but he was told to do it with the Western methods.

    So Galileo’s science spread to China only twenty years after Galileo began his work; even six years after, in 1615, there were books in Chinese, written by Jesuits, telling about Galileo’s discoveries, with illustrations of the telescope and so on. Which is pretty fast, if you think about it!

    The standard picture of a conflict between science and religion doesn’t really hold up, especially if you look at the history of the Jesuits and astronomy.

    Absolutely. They had a very special role in the church. You know, they were disbanded at the end of 1700; there were conflicts between them and the Franciscans, including in China. The Jesuits were not very strict; they were eager to culturally adapt themselves, wearing Chinese clothes and so on. And the Franciscans were much more strict; they didn’t want to make cultural compromises. So there was this conflict between these two ways of spreading religion, and finally the Franciscans had their way.

    Do you know the American physicist Stephen Barr? He’s Catholic and he’s done a lot of work challenging the idea of the conflict between science and religion. One of the things he focuses on is different views of causality; for example, the difference between a traditional Thomistic account of cause and the Newtonian, or post-Newtonian, account of cause.

    We were talking earlier about all these entirely speculative models of pre-Big Bang cosmology, the Bouncing Universe, or multiple-universe cosmology and so on. Even if any of those were true, it still would not exhaust the idea of a cause in the way Saint Thomas and the scholastics were thinking about causes. Saint Thomas thought it was impossible to tell through purely philosophical inquiry whether the universe had a beginning, though he believed based on Scripture that it did, and, with Augustine, conceived of the beginning of the material cosmos and of time as simultaneous. He would not have been surprised, that is, at the Big Bang hypothesis. But the idea that God in time, sequentially, started things off is not the only cause that he was dealing with. That idea looks at God as the efficient cause of the universe, but to look at him only as the efficient cause is to reduce him to the god of the Deists. Saint Thomas also emphasized God as the final cause, the reason why the universe was formed, and as the one from whom the universe derived its being at every moment.

    That’s the level at which I’m really interested in trying to see the universe as a Cosmos. For Dante, astronomy was a kind of contemplative art – in Canto 33 of the Paradiso, the contemplation of God is of something astronomical; there’s even a sense in which God looks like math.

    Or like light.

    yellow colorized etching of rings of angels around two figures on a cloud illustrating Dantes work

    Gustave Doré, Heavenly Host, colorized Image public domain

    Right. In your work as an astronomer, do you find that contemplative aspect? Do you see beauty?

    Beauty? I do. But again, it’s a question of approach. For example, if you see a rainbow, you can look at the rainbow and get astonished, admire it, perhaps think there is a pot of gold at the end of it! Which is very satisfactory. And the other way is to ask, why is the rainbow there? There is a scientific explanation, of course – it’s the diffraction of light through drops of water. And the same person can do both. And you need both: in the scientific approach, you lose some of the beauty, because you are taking it apart.

    You’re talking about an analytic versus a holistic way of approaching things.

    Yes, if you like. Dante speaks several times of the rainbow. For example, in Canto 29 of the Purgatorio, to describe the bright colors of the luminous trails left by the seven candelabra carried in procession, shortly before the meeting with Beatrice, he refers to the rainbow and to the moon halo. (The Moon is mythologically assimilated to Diana – in Greek Artemis – who was born in Delos, and is here called Delia for her birthplace.)

    … e vidi le fiammelle andar davante,
    lasciando dietro a sé l’aere dipinto,
    e di tratti pennelli avean sembiante;
    … sì che lì sopra rimanea distinto
    di sette liste, tutte in quei colori
    onde fa l’arco il Sole e Delia il cinto.

    (Pur. XXIX, 73–78)

    “And I saw the flames move on, leaving the air behind them painted, and they seemed like brushes drawn along, so that the air overhead was marked with seven stripes, all in those colors with which the Sun makes his bow and Delia her belt.”

    This metaphor is scientifically very appropriate, because in both cases the colors are due to reflections within drops of water. In Canto 25 of the Purgatorio, he mentions the fact that the rainbow is due, as we well know, to the reflection of the sun’s rays in the raindrops:

    … E come l’aere, quand’è ben pïorno,
    per l’altrui raggio che ‘n sé si reflette,
    di diversi color diventa addorno …

    (Pur. XXV, 91–93)

    “And just as the air, when it is very moist, becomes adorned with various colors because it reflects another’s rays …”

    Again in Canto 12 of the Paradiso the poet, to describe the double crown of spirits that appeared during the speech of Thomas Aquinas, uses the double arc of the rainbow:

    … Come si volgon per tenera nube
    due archi paralleli e concolori,
    quando Iunone a sua ancella iube,
    … nascendo di quel d’entro quel di fori,
    a guisa del parlar di quella vaga
    ch’amor consunse come sol vapori,
    … e fanno qui la gente esser presaga,
    per lo patto che Dio con Noè puose,
    del mondo che già mai più non s’allaga …

    (Par. XII, 10–18)

    “As through a tenuous cloud two arcs curve parallel and colored alike, when Juno commands her handmaid, the outer born from the inner one, like the speech of that desirous nymph whom love consumed as the sun does vapors, and cause people here to predict the weather, thanks to the pact God made with Noah, that the world will never again be flooded …”

    This representation of the phenomenon is very accurate. It occurs with the sun behind the observer, who has the rain in front, so the solar light is projected onto the clouds that produce the rain. In addition, the two arcs are concentric, that is, parallel, and the colors are repeated in reverse (“the outer born from the inner one”), since the external arc of a double rainbow is due to a double reflection in the raindrops. The rainbow nymph Iris, who was Juno’s handmaid, is accompanied by the nymph Echo, who was consumed with love for Narcissus. To these pagan memories Dante adds the biblical one of the rainbow, which marks God’s reconciliation with humanity after the punishment of the universal flood and seals the pact with Noah that there would be no other total floods.

    You’ve said that you used to think that only the scientific understanding of the world was valid, but that you’ve moved away from that kind of scientism – what has that movement been like? Has it been related to getting more involved in your ancestor’s work? Or is it a separate thing?

    I think it’s separate, although it may have to do with the same evolution of mind, in a sense. It’s difficult to say. There are various aspects of this. One of them is that a scientist will do his best work when he’s very young. I mean, after thirty or thirty-five, it’s very difficult to make important new discoveries. This is demonstrated by history: all scientists make their best discoveries when they’re young: Einstein, Newton, Galileo. This is because the mind evolves.

    The nasty way to view it is that every second we lose – I don’t know how many – neurons, but many, so evolution is a bit more like involution. Of course, the evolution of mind is not just a loss of neurons. There’s also experience. A boy when he is born has plenty of neurons, but no experience; he can’t even talk, because he hasn’t learned. So there has to be a mix between intellectual capability and experience.

    The patterns that we form, the wisdom that we form.

    Yes. So after thirty or thirty-five, you lose a certain kind of genius in the sense of making new scientific discoveries, but you gain experience, and that gives you some advantages as you grow older. But the advantages are in the area, if you like, of accepting certain things with which maybe before you had problems.

    And that was how it was for me with religion, in some ways, and accepting being a descendant of Dante in some other ways. The two things are connected because of this but not necessarily connected for other reasons. Timewise, I think I approached religion before I approached Dante, but I’m not sure.

    Are you a practicing Catholic now? Do you go to Mass?

    Yes, I am now. I had a turning point about ten years ago – you know, it actually was about the same time as my interest in Dante. I hadn’t thought about this! But it was a turning point. Maybe by chance.

    You found yourself in a dark wood?

    Actually, it was because our daughter was getting married. Not quite ten years ago. Laura. We have an older son, Pietro, born in 1981; then Laura was born two and a half years later. Now Pietro has a son, Leonardo, who is eleven years old: he was born in 2010. Pietro and Virginia, Leonardo’s mother, are still very much together, but they are not married, so we didn’t have a wedding. We had a grandson, but not a wedding! But with Laura, she wanted to get married properly, in the church. Where I live now, in Perugia, is a family house from 1600 or so, and in it there is a small Catholic chapel, which is still consecrated; you can still have Mass there, which we do, not every Sunday, but a few times in the year. So Laura wanted to marry in that chapel, and as I was getting it ready, it was that moment when I found that I needed to now decide what to do about this, about my religion. So that was a turning point.

    For Dante, what was the turning point? I don’t know … Well, yes, I do, actually. That happened slightly before. When I started working, we went to the Netherlands, and our children were born in the Netherlands; then we went to Germany, and eventually then we came back to Italy. That was the beginning of the 1990s, when I began to work in Arcetri, in the observatory in Florence.

    I shared an office in Arcetri with a colleague who was very fond of Dante, and he had a friend, also at the observatory, an engineer, who was very interested in Dante’s cosmology. And every afternoon the three of us had teatime together. And we got to talk about Dante, of course. In the beginning, I was not so interested. They would say, “But you are descended!” And I would say, “yeah, well, OK.” But then I got interested: their interest drew me. Also, my colleague was giving lessons at the planetarium in downtown Florence, and he got me into doing that too. I liked that very much. And that made me closer to Dante, because one of the lessons I had to give was about Dante’s astronomy.

    But it was only ten years ago that I really began to learn more about Dante’s cosmology, that’s when I really got interested. And why that timing? I don’t know.

    Thank you so much for all the time! May I ask you one more thing? Will you read the last part of Canto 33 of the Paradiso aloud to me?

    I will have to find it – here, I’ll read from here:

    A l’alta fantasia qui mancò possa;
    ma già volgeva il mio disio e ‘l velle,
    sì come rota ch’igualmente è mossa,
    l’amor che move il sole e l’altre stelle.

    Here my powers rest from their high fantasy,
    but already I could feel my being turned—
    instinct and intellect balanced equally

    as in a wheel whose motion nothing jars—
    by the Love that moves the Sun and the other stars.


    Interview conducted by Susannah Black.

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