A subgame-perfect equilibrium is a strategy profile that induces a Nash equilibrium in every subgame
of a sequential game, including subgames
that are not reached during equilibrium play. It therefore rules out noncredible
threats that depend on irrational behavior after an off-equilibrium move.
Selten, R. "Spieltheoretische Behandlung eines Oligopolmodells mit Nachfrageträgheit." Z. Gesamte Staatswiss.121, 301-324,
1965. https://doi.org/10.1007/BF01737558.
