let x be RelStr ; :: according to WAYBEL_3:def 8 :: thesis: ( not x in proj2 <%P,Q%> or x is reflexive )
assume x in rng <%P,Q%> ; :: thesis: x is reflexive
then x in {P,Q} by Lm3;
hence x is reflexive by TARSKI:def 2; :: thesis: verum