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_15, x_15 will take a plane if and only if x_15 is a sailor. There is at least one x_15 for which x_15 is a sailor if and only if x_15 will go running. For all x_15, if x_15 takes a plane, then x_15 is running.
For all x_15, if x_15 takes a plane, then x_15 is a sailor can be inferred via the universal biconditional elimination rule. There is at least one x_15 for which if x_15 were a sailor, then x_15 is running can be inferred via the existential biconditional elimination rule. For all x_15, if x_15 were a sailor, then x_15 is taking a plane can be inferred via the universal biconditional elimination rule. There is at least one x_15 for which if x_15 goes running, then x_15 is a sailor can be inferred via the existential biconditional elimination rule.