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 x_6, x_6 will listen to a song if and only if x_6 will drink water. For all x_6, if x_6 climbs a mountain, then x_6 is drinking water. For all x_6, x_6 will not write a letter or x_6 will listen to a song. There is at least one x_6 for which x_6 will write a letter or x_6 will climb a mountain.
There is at least one x_6 for which x_6 will climb a mountain or x_6 will listen to a song can be inferred via the existential resolution rule. For all x_6, if x_6 listens to a song, then x_6 is drinking water can be inferred via the universal biconditional elimination rule. For all x_6, if x_6 drinks water, then x_6 is listening to a song can be inferred via the universal biconditional elimination rule.