
theorem
  for S1,S2 being non empty ManySortedSign for x being set st x in
  InnerVertices S2 holds x in InnerVertices (S1+*S2)
proof
  let S1,S2 be non empty ManySortedSign;
  set R1 = the ResultSort of S1, R2 = the ResultSort of S2;
  InnerVertices (S1+*S2) = rng (R1+*R2) by CIRCCOMB:def 2;
  then InnerVertices S2 c= InnerVertices (S1+*S2) by FUNCT_4:18;
  hence thesis;
end;
