MAYBE

Problem:
 bsort(nil()) -> nil()
 bsort(.(x,y)) -> last(.(bubble(.(x,y)),bsort(butlast(bubble(.(x,y))))))
 bubble(nil()) -> nil()
 bubble(.(x,nil())) -> .(x,nil())
 bubble(.(x,.(y,z))) -> if(<=(x,y),.(y,bubble(.(x,z))),.(x,bubble(.(y,z))))
 last(nil()) -> 0()
 last(.(x,nil())) -> x
 last(.(x,.(y,z))) -> last(.(y,z))
 butlast(nil()) -> nil()
 butlast(.(x,nil())) -> nil()
 butlast(.(x,.(y,z))) -> .(x,butlast(.(y,z)))

Proof:
 Open