The Elements

...not [to] have equal bases, but [those] in the same [parallels], or equal [ones] to be given through point Β. [Draw] an angle equal to ΒΓΔ. And the rest is clear.

Two small geometric diagrams: on the left, two lines meeting at an angle with points labeled; on the right, two triangles sharing a vertex, used to demonstrate angle construction.

If into two equal [lines] from the same point, point Β, oblique angles are made equal, then of necessity the remaining angles, along which the intervals create the [line] toward the straight line [those] of point Β, [are equal] to the [angles] toward the greater angle being right or contained; for if the oblique [line] toward point Δ is not right, but some other [line] toward the same [point] toward point Β, it is clear that [it is] not toward Γ... and the angles are not equal; but toward Γ, from the [angle] produced, the angle ΒΓΔ is equal to [it] at Β. And the angle ΒΖΔ is also given. In the triangle, each is equal to each. Either [it] is an acute angle toward Γ, and the angle ΑΒΓ is contained by the one following [it]; for the one following [it], being any [angle], each of the following angles are equal to one another [as] right [angles]. And the rest of these are clear. And another of the equal oblique angles... they coincide upon the same things.

A geometric diagram of a triangle ABC with a vertical perpendicular line dropped from vertex B to the base AC, meeting at point D. The base line extends horizontally through points A, D, and C, with labels in Greek script.

Circular institutional library stamp (likely Bibliothèque Nationale) at the bottom right of the text block.