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BOOK I. PROP. XIX. THEOR.
19
F in any triangle 
one angle 
be greater than another 
the side 
which is opposite to the greater angle, is greater than the side 
opposite the less.
If be not greater than then must
= or < .
If = then = (pr. 5.); which is contrary to the hypothesis.
is not less than for if it were, < (pr. 18.) which is contrary to the hypothesis:
∴ > .
Q.E.D.
