export fact

fact c n :=
    f =
        call == fact
        drop c := c
    copy_int n -> n1 n2
    one -> o
    try_minus n1 o ->
        ok n :=
            c = _ n :=
                mul n n2 -> n
                c n
            f.call c n
        err n o :=
            drop_int n ->
            drop_int n2 ->
            f.drop ->
            c o