Triangle their internal angles, measured here in degrees. A triangle that has two angles with the same measure also has two sides with the same length, and therefore it is an isosceles triangle. It follows that in a triangle where all angles have the same measure, all three sides have the same length, and such a triangle is therefore equilateral. Triangles are assumed to be two-dimensional plane figures, unless the context provides otherwise (see Non-planar triangles, below). In rigorous treatments, a triangle is therefore called a "2-simplex" (see also Polytope). Elementary facts about triangles were presented by Euclid in books 1–4
West Africa: Word, Symbol, Song for previously held misconceptions about West Africa", and "The Cultural Exposé" concluded: "So if there was ever a question about the significance of Africa to the development of culture and civilisation, this exhibition is a metaphorical bomb drop. Prepare to be enlightened." The book "West Africa: Word, Symbol, Song", edited by Gus Casely-Hayford, Janet Topp Fargion and Marion Wallace, was produced by the British Library to accompany the exhibition. In 2018, in partnership with the British Library, the Aké Arts and Book Festival in Lagos, Nigeria, presented digital highlights of the exhibition in a "Memory Room". West Africa: Word, Symbol,