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 x_21 for which x_21 will go running. For all x_21, if x_21 plays tennis, then x_21 is an artist. For all x_21, if x_21 listens to a song, then x_21 is happy. For all x_21, x_21 will play tennis if and only if x_21 is happy. For all x_21, if x_21 goes running, then x_21 is listening to a song.
There is at least one x_21 for which x_21 will listen to a song can be inferred via the existential modus ponens rule. For all x_21, if x_21 goes running, then x_21 is happy can be inferred via the universal transitivity rule. For all x_21, if x_21 plays tennis, then x_21 is happy can be inferred via the universal biconditional elimination rule. For all x_21, if x_21 were happy, then x_21 is playing tennis can be inferred via the universal biconditional elimination rule.