intersect = a b + res ->
  contains -a = a i + extsts ->                                                ++- Nested function
    for a x ->
      if (x = i) -> exists = 1, leave
      else iterate
    ;
  ;

  for b i ->                                                                   ++- "intersect()" begins here...
    if (a->contains i) -> attach res i
  ;
_
  a, b : array
;