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_13, if x_13 were a cashier, then x_13 is playing tennis. For all x_13, x_13 is a cashier. For all x_13, x_13 is sad. There is at least one x_13 for which if x_13 plays tennis, then x_13 is climbing a mountain.
For all x_13, x_13 will play tennis can be inferred via the universal modus ponens rule. There is at least one x_13 for which if x_13 were a cashier, then x_13 is climbing a mountain can be inferred via the existential transitivity rule. For all x_13, x_13 is a cashier and x_13 is sad can be inferred via the universal conjunction rule. For all x_13, x_13 is sad and x_13 is a cashier can be inferred via the universal conjunction rule.