Paste: forthus anti prelude

     a = hd
     b = hd tl
     c = hd tl tl
    sq = *[id, id]
    0? = eq?[id, 0]
  succ = +[id, 1]
  pred = -[id, 1]
   neg = *[id, -1]
    or = if[b, a, (true), (id)]
small? = or[0?, eq?[id, 1]]
  fact = if[id, 0?, (1), (*[id, fact pred])]
   fib = if[id, small?, (1), (+[fib pred, fib -[id, 2]])]
 twice = i[a, i]
double = +[id, id]
quadro = twice[(double), id]
    // = [/[a a, b], /[b a, b]]
 discr = -[sq b, *[4, *[a, c]]]
 roots = //[[+, -][neg b, sqrt discr], *[2, a]]
 null? = eq?[id, []]
   map = if[id, null? b, ([]), (cons[i[a, hd b], map[a, tl b]])]
  fold = if[id, null? c, (b), (fold[a, i[a, [b, hd c]], tl c])]
   sum = fold[(+), 0, id]