Consistency checks (same as in Container).
Container
M : Accessors_generic with type (a, b, c) options := (a, b, c) Options.t with type (a, b, c) t := (a, b, c) T.t with type (a, b, c) tree := (a, b, c) Tree.t with type a key := a Key.t
Options : Base.T.T3
Key : Base.T.T1
Tree : Base.T.T3
T : Base.T.T3