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 y, y is sad if and only if y will play squash. For all y, if y plays squash, then y is sad. There is at least one y for which y will not play squash.
For all y, if y were sad, then y is playing squash can be inferred via the universal biconditional elimination rule. For all y, if y plays squash, then y is sad can be inferred via the universal biconditional elimination rule. There is at least one y for which y is not sad can be inferred via the existential biconditional elimination rule.