FiniteSimplicialSet

A finite simplicial set presented by generators (non-degenerate simplices) and, for each generator, its primitive face data -- from which everything else (arbitrary d_i/s_j, the OrderedCell instance feeding the homology engines) is inferred via faceOf/insertOuter (SSetElement.scala).

faces(g), for g of dimension n, must supply exactly n+1 already-normalized SSetElements of dimension n-1 each (empty for n = 0) -- validate() checks this contract plus the simplicial identities at runtime, since it's easy to get a hand-written presentation subtly wrong with no crash, just silently wrong homology.