(Edited by Dionysius Lardner, 1855)

Proposition XXX. Theorem.

[Euclid, ed. Lardner, 1855, on `Google Books`]

(121) | If two right lines (A B, C D) be parallel to the same right line (E F), they are parallel to each other. |

Book I: Euclid, Book I (ed. Dionysius Lardner, 11th Edition, 1855)

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This proposition in other editions:

(122) Cor.—Hence two parallels to the same line cannot pass through the same point. This is, in fact, equivalent to the twelfth axiom (115).