H
E
E
L
E
M
E
N
T
S
Therefore
[when a straight line EF falling on the two straight lines AB, CD make the alternate angles AEF, EFD equal to one another,] AB is parallel to CD.
Being what it was required to prove.
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T H E E L E M E N T S |
Book I Proposition 27 | |
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But straight lines which do not meet in either direction are parallel. [Def.23] Therefore [when a straight line EF falling on the two straight lines AB, CD make the alternate angles AEF, EFD equal to one another,] AB is parallel to CD. Being what it was required to prove. |
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