In the context of finite extensive form games, we consider games of imperfect and perfect recall. We look briefly at the famous Kuhn theorem. However we are mainly concerned with imperfect recall games in which paths can intersect information sets in more than one node. Explicit examples are given to examine a number of issues. We explain how optimal behaviour strategies are calculated. It is also argued that mixed behavioural strategies cannot always be captured by a behavioural strategy. We are considering the existence of a Nash equilibrium both in the case of mixed and of behavioural strategies. In order to make the discussion possible, starting with the players expected utilities in behavioural strategies in a polynomial form, a precise construction of a game tree is presented. In the case of existence of NE the solutions can imply identical or different pay-off vectors. A reference is also made to the recent discussion on the paradox of the absent-minded driver.