main =>
  L = a(1000),
  println(L[1..10]),
  println(L[991..1000]),
  nl.

a(0) = {0}.
a(1) = {0,0}.
a(N) = A ++ {cond(M > 0, N-M, 0)} =>
  A = a(N-1),
  M = find_last_of(slice(A,1,N-1),A.last).