Assertion: polyhedron's number | /r/CapableOf | call euler characteristic
Facets:
Source sentences:
text: Then we notice that a number can be assigned to any polytope (and a number of other things) called its Euler characteristic ( c ), which is additive for disjoint sets, equal to 1 for a point and invariant in a topological homeomorphism (so that topologically equivalent things have the same c ).
text: It turns out that this number, called the Euler characteristic, is crucial to the study of all three-dimensional surfaces, not just polyhedra.