What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Name the inference rule being used: For all x_5, if x_5 were a sailor, then x_5 is playing a game. For all x_5, if x_5 plays a game, then x_5 is a sailor. There is at least one x_5 for which x_5 is not a sailor.
There is at least one x_5 for which x_5 will not play a game can be inferred via the existential modus tollens rule. For all x_5, x_5 is a sailor if and only if x_5 will play a game can be inferred via the universal biconditional introduction rule. For all x_5, x_5 will play a game if and only if x_5 is a sailor can be inferred via the universal biconditional introduction rule.