boolean := *top*.

true := boolean.
  
false:= boolean. 
 
string :=  *top*. 
;;;"A special type which any lisp string will unify". 
 
 
;;;"Do append eqvnt without recursive types" 
diff-list := *top* & 
[ LST list, 
  LAST list ]. 
 
list := *top*. 
 
e-list := list. 
 
ne-list := list & 
[HD *top*, 
 TL list].