theorem Th14:
  E-min C in C & E-max C in C
proof
A1: E-min C in E-most C by PSCOMP_1:50;
A2: E-max C in E-most C by PSCOMP_1:50;
  E-most C c= C by XBOOLE_1:17;
  hence thesis by A1,A2;
end;
