Assertion: polyhedron's vertex | /r/HasProperty | less than π radians
Facets:
Source sentences:
text: In a polygon, a vertex is called "convex" if the internal angle of the polygon, that is, the angle formed by the two edges at the vertex, with the polygon inside the angle, is less than π radians ( 180°, two right angles) ; otherwise, it is called "concave" or "reflex".