  We revisit and reinterpret Selten's concept of subgame perfectness in the
context of single agent normal form sequential decision making, which leads us
to the concept of subtree perfectness. Thereby, we extend Hammond's
characterization of extensive form consequentialist consistent behaviour norms
to the normal form and to arbitrary choice functions under very few
assumptions. In particular, we do not need to assume probabilities on any event
or utilities on any reward. We show that subtree perfectness is equivalent to
normal-extensive form equivalence, and is sufficient, but, perhaps
surprisingly, not necessary, for backward induction to work.
