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: John is writing a letter or William is climbing a mountain. For all y, y is a poet if and only if y will write a letter. If William climbs a mountain, then John is a poet.
For all y, if y were a poet, 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 a poet can be inferred via the universal biconditional elimination rule.