fact: Definition join {A: Type} (k1: key) (t1: ptrie A) (k2: key) (t2: ptrie A) := let m := branching_bit k1 k2 in if zerobit k1 m then Branch (mask k1 m) m t1 t2 else Branch (mask k1 m) m t2 t1.
imports: List Bool ZArith Lia