T
H
E

E
L
E
M
E
N
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Book I   Proposition 4
Therefore
    the base BC will coincide with EF and will be equal to it. [C.N.4]
Thus
    the whole triangle ABC will coincide with the whole triangle DEF, and will be equal to it.

And the remaining angles will also coincide with the remaining angles and will be equal to them,
    the angle ABC to the angle DEF, and the angle ACB to the angle DFE.

Being what it was required to prove.
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