The first half of the antiphon O admirabile commercium (Cantus ID 003985) is quoted in the T (passage: "O admirabile ... et procedens homo") and partially in the C (incipit):

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"O admirabile commercium creator generis humani"

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"animatum corpus sumens de virgine"

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"nasci dignatus est et procedens homo" (http://cantusindex.org/id/003985)

The next part of the antiphon O admirabile commercium (Cantus ID 003985) is quoted in the C (passage "sine semine")

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"sine semine" (http://cantusindex.org/id/003985)

The last part of the antiphon O admirabile commercium (Cantus ID 003985) is quoted in the T (passage "largitus est" ... end)

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"largitus est nobis suam deitatem" (http://cantusindex.org/id/003985)