
theorem Th4:
  for R being non empty reflexive RelStr,
      x being Element of R holds
    x in Class (the InternalRel of R,x)
  proof
    let R be non empty reflexive RelStr;
    let x be Element of R;
A1: x in field the InternalRel of R by Th1;
A2: x in {x} by TARSKI:def 1;
    [x,x] in the InternalRel of R by A1,RELAT_2:def 1,RELAT_2:def 9;
    hence thesis by RELAT_1:def 13,A2;
  end;
