Euler 1758 V - E + F = 2 for 3-polytopes; Schlafli 1850 generalization to any d; basis of polyhedral combinatorics + simplicial complex topology.
Euler 1758 V - E + F = 2 for 3-polytopes; Schlafli 1850 generalization to any d; basis of polyhedral combinatorics + simplicial complex topology.