reserve T, X, Y for Subset of MC-wff;
reserve p, q, r, s for Element of MC-wff;
reserve T, X, Y for Subset of MC-wff;
reserve p, q, r for Element of MC-wff;
reserve T, X, Y for Subset of MC-wff;
reserve p, q, r for Element of MC-wff;

theorem Th81:
  CnIPC (X) c= CnS4 (X)
proof
A1: CnCPC (X) c= CnS4 (X) by Th80;
  CnIPC (X) c= CnCPC (X) by Th68;
  hence thesis by A1;
end;
