T H E E L E M E N T S |
Book I Proposition 1 | |
AC was proved equal to AB and BC was proved equal to BA. Therefore each of the straight lines CA, CB is equal to AB. And things which are equal to the same thing are also equal to one another [C.N.1]; therefore CA is also equal to CB. Therefore the three straight lines CA, AB, BC are equal to one another. |
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