reserve Y for non empty set;
reserve Y for non empty set;
reserve Y for non empty set;
reserve Y for non empty set,
  a,b,c,d,e,f,g for Function of Y,BOOLEAN;

theorem
  a '&' b '&' c '&' d '&' e '<' a & a '&' b '&' c '&' d '&' e '<' b by Lm4;
