def _fibin
def _fibout
f fib
    def tmp def pov def a def b
    = pov 0

    = tmp = _fibin 1
    if tmp    = pov 1    .

    = tmp = _fibin 2
    if tmp    = pov 1   .

    = _fibout pov
    = tmp - pov 1

    if tmp
        = a - _fibin 1
        = b - a 1
        = _fibin a   call fib   = a _fibout
        = _fibin b   call fib   = b _fibout
        = _fibout + a b
    .
.
inc _fibin
call fib
out _fibout