biangle

plural biangles

1. A digon or bigon; a two-sided shape (especially in non-Euclidean geometry)

   Then the right biangle CABD and the oblique biangle CPND are equivalent since the triangles API and BNI are congruent.

   1912, Proceedings of the Edinburgh Mathematical Society, volumes 30-32, Scottish Academic Press, page 35

   2 more examples

   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.

   1895, W. Burnside, “Kinematics of Non-Euclidean Space”, in Proceedings of the Edinburgh Mathematical Society, page 46

   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.

   2012 December 6, Gerold Prauss, “Kant and the Straight Biangle”, in Enno Rudolph, Ion-Olimpiu Stamatescu, editors, Philosophy, Mathematics and Modern Physics: A Dialogue, page 228

   Synonyms: digon, bigon, diangle