f(n)=
  ? n=0, <= 1
  <= n-m(f(n-1))
.
m(n)=
  ? n=0, <= 0
  <= n-f(m(n-1))
.
> i, 0..20
  fs += " "+f(i)
  ms += " "+m(i)
<
#.output("F:",fs)
#.output("M:",ms)