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_12, if x_12 writes a letter, then x_12 is climbing a mountain. For all x_12, x_12 will listen to a song or x_12 will write a letter. For all x_12, if x_12 takes a plane, then x_12 is a taxi driver. There is at least one x_12 for which if x_12 listens to a song, then x_12 is climbing a mountain. For all x_12, x_12 will take a plane.
For all x_12, x_12 is a taxi driver can be inferred via the universal modus ponens rule. There is at least one x_12 for which x_12 will climb a mountain can be inferred via the existential disjunction elimination rule.