If two right lines cut one another, they will form the...

If two right lines cut one another, they will form the angles at the vertex equal....
This... is what the the present theorem evinces, that when two right lines mutually cut each other, the vertical angles are equal. And it was first invented according to Eudemus by Thales...

Proposition XV. Thereom VIII. - The Philosophical and Mathematical Commentaries of Proclus on the First Book of Euclid's Elements Vol. 2 (1789)

If two right lines cut one another, they will form the angles at the vertex equal.... This... is what the the present theorem evinces, that when two...

If two right lines cut one another, they will form the angles at the vertex equal.... This... is what the the present theorem evinces, that when two...

If two right lines cut one another, they will form the angles at the vertex equal.... This... is what the the present theorem evinces, that when two...

If two right lines cut one another, they will form the angles at the vertex equal.... This... is what the the present theorem evinces, that when two...