`lset<=``=``list_1``...`procedureReturns true iff every LIST_I is a subset of LIST_I+1, using = for the element-equality procedure. List A is a subset of list B if every element in A is equal to some element of B. When performing an element comparison, the = procedure's first argument is an element of A; its second, an element of B.

(lset<= eq? '(a) '(a b a) '(a b c c)) => #t (lset<= eq?) => #t ; Trivial cases (lset<= eq? '(a)) => #t