In his work on signaling, Spence proposed a dynamic model of a market in which a buyer revises prices in light of experience and in which sellers, with private information about their type, choose utility-maximizing signals given these prices. We follows Spence's suggestion of introducing...

A strategy profile of a normal form game is proper if and only if it is quas-perfect in every extensive form (with that normal form). Thus, properness requires optimality along a sequency of supporting trembles, while sequentiality only requires optimality in the limit.