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 z, if z were a mechanic, then z is playing tennis. For all x_13, if x_13 writes a letter, then x_13 is a mechanic. For all x_13, x_13 will write a letter or x_13 will listen to a song. For all x_13, x_13 will listen to a song if and only if x_13 is a mechanic.
For all x_13, if x_13 listens to a song, then x_13 is a mechanic can be inferred via the universal biconditional elimination rule. For all x_13, if x_13 were a mechanic, then x_13 is listening to a song can be inferred via the universal biconditional elimination rule.