reserve U for Universe;
reserve x for Element of U;
reserve U1,U2 for Universe;

theorem Th85:
  for C being CategorySet holds C is non empty
  proof
    let C be CategorySet;
    consider x1,x2,x3,x4,x5 be object such that
A1: C = [x1,x2,x3,x4,x5] by Def3;
    assume C is empty;
    hence thesis by A1;
  end;
