theorem Th11:
  N-min C in C & N-max C in C
proof
A1: N-min C in N-most C by PSCOMP_1:42;
A2: N-max C in N-most C by PSCOMP_1:42;
  N-most C c= C by XBOOLE_1:17;
  hence thesis by A1,A2;
end;
