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Euler's classical formula for convex polyhedra
$$v-e+f=0$$$$v-e+f=2$$
where $v$ is the number of vertices, $e$ the number of edges and $f$ the number of faces of a convex triagulated polyhedron in $3$-space.
Euler's classical formula for polyhedra
$$v-e+f=0$$
where $v$ is the number of vertices, $e$ the number of edges and $f$ the number of faces of a triagulated polyhedron in $3$-space.
$$v-e+f=2$$
