let or      := map x,y to if x then true else y;
       member  := map x,l to if null?(l) then false
                             else or(x = first(l), member(x, rest(l)));
   in member (1, cons(1, null))

=> let ... in (map x, l to ...)(1, cons(1, null))
=> let ... in if null?(cons(1,null)) then false
              else or(1 = first(cons(1,null)), member(1,rest(cons(1,null))))
=> let ... in if false then false
              else or(1 = first(cons(1,null)), member(1,rest(cons(1,null))))
=> let ... in or(1 = first(cons(1,null)), member(1,rest(cons(1,null))))
=> let ... in (map x,y to ...)(1 = first(cons(1,null)), member(1,rest(cons(1,null))))
=> let ... in (map x,y to ...)(1 = 1, member(1,rest(cons(1,null))))
=> let ... in (map x,y to ...)(true, member(1,rest(cons(1,null))))
=> let ... in (map x,y to ...)(true, (map x,l to ...)(1,rest(cons(1,null))))
=> let ... in (map x,y to ...)(true, (map x,l to ...)(1,null))
=> let ... in (map x,y to ...)(true, if null?(null) then false
                                     else or(1 = first(null), member(1,rest(null))))
=> let ... in (map x,y to ...)(true, if true then false
                                     else or(1 = first(null), member(1,rest(null))))
=> let ... in (map x,y to ...)(true, false)
=> let ... in if true then true else false
=> let ... in true
=> true