reserve n for Nat,
  k for Integer;
reserve p for polyhedron,
  k for Integer,
  n for Nat;

theorem Th73:
  for x being Element of (dim(p)-1)-polytopes(p), c being Element
  of dim(p)-chain-space(p) st c = {p} holds Sum incidence-sequence(x,c) = 1.Z_2
proof
  let x be Element of (dim(p)-1)-polytopes(p), c be Element of dim(p)
  -chain-space(p);
  assume c = {p};
  then incidence-sequence(x,c) = <*1.Z_2*> by Th72;
  hence thesis by FINSOP_1:11;
end;
