a boundary is a mean of old / child toad
duttaphrynus is toad. tree_toad is frog. pelophryne is toad. fire_bellied_toad is toad. tree_toad is not frog. western_narrow_mouthed_toad is frog. western_narrow_mouthed_toad is not frog. rococo_toad is toad. mongolian_toad is toad. toad is not anura.