reserve c,c1,c2,x,y,z,z1,z2 for set;
reserve C1,C2,C3 for non empty set;

theorem
  for f,g be RMembership_Func of C1,C2 holds converse(f\g) = (converse f
  )\(converse g)
proof
  let f,g be RMembership_Func of C1,C2;
  converse(f\g) = min(converse f,converse 1_minus g) by Th8
    .= min(converse f,1_minus converse g) by Th6;
  hence thesis;
end;
