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: There is at least one y for which y will play squash. For all y, if y listens to a song, then y is drinking water. For all y, y will listen to a song or y will write a letter. For all y, y will drink water if and only if y will write a letter. For all y, if y drinks water, then y is writing a letter.
For all y, if y listens to a song, then y is writing a letter can be inferred via the universal transitivity rule. For all y, if y drinks water, then y is writing a letter can be inferred via the universal biconditional elimination rule. For all y, if y writes a letter, then y is drinking water can be inferred via the universal biconditional elimination rule.