theorem Th137:
  a in variables_in H implies a <> 0 & a <> 1 & a <> 2 & a <> 3 & a <> 4
proof
  assume a in variables_in H;
  then not a in {0,1,2,3,4} by XBOOLE_0:def 5;
  then not a in {0,1} \/ {2,3,4} by ENUMSET1:8;
  then ( not a in {0,1})& not a in {2,3,4} by XBOOLE_0:def 3;
  hence thesis by ENUMSET1:def 1,TARSKI:def 2;
end;
