# biangle

## English

### Etymology

From bi- +‎ angle.

### Noun

biangle

1. A digon or bigon; a two-sided shape (especially in non-Euclidean geometry)
• 1895, W. Burnside, “Kinematics of Non-Euclidean Space”, in Proceedings of the Edinburgh Mathematical Society[1], page 46:
If n planes be drawn through any axis of the right-vector, each of which makes angles π/n with the planes on either side of it, the whole of space is divided into n congruent figures which may be called biangles, the space between any two adjacent planes being easily seen to be continuous with the vertically opposite space between them.
• 1912, Proceedings of the Edinburgh Mathematical Society[2], Scottish Academic Press, page 35:
Then the right biangle CABD and the oblique biangle CPND are equivalent since the triangles API and BNI are congruent.
• 2012 December 6, Gerold Prauss, “Kant and the Straight Biangle”, in Enno Rudolph; Ion-Olimpiu Stamatescu, editors, Philosophy, Mathematics and Modern Physics: A Dialogue[3], page 228:
It is therefore natural to consider whether precisely this concept of a straight line, with which Kant11 too was familiar, is the reason why Kant in the one passage says that the concept of a straight biangle is free of contradiction.