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: Linda is not taking a plane. For all y_2, if y_2 plays squash, then y_2 is taking a plane. For all y_2, if y_2 takes a plane, then y_2 is playing squash. Linda is playing squash if and only if David is a server.
If Linda plays squash, then David is a server can be inferred via the biconditional elimination rule. If David were a server, then Linda is playing squash can be inferred via the biconditional elimination rule. For all y_2, y_2 will play squash if and only if y_2 will take a plane can be inferred via the universal biconditional introduction rule. For all y_2, y_2 will take a plane if and only if y_2 will play squash can be inferred via the universal biconditional introduction rule.