theorem Th136:
  not x in { 0,1,2,3,4 }
proof
  assume x in { 0,1,2,3,4 };
  then x in { 0,1 } \/ { 2,3,4 } by ENUMSET1:8;
  then x in { 0,1 } or x in { 2,3,4 } by XBOOLE_0:def 3;
  then
A1: x = 0 or x = 1 or x = 2 or x = 3 or x = 4 by ENUMSET1:def 1,TARSKI:def 2;
  x in VAR;
  then ex i st x = i & 5 <= i;
  hence contradiction by A1;
end;
