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_4, x_4 will play squash or x_4 is an office clerk. For all x_4, if x_4 were an office clerk, then x_4 is climbing a mountain. There is at least one x_4 for which if x_4 were a writer, then x_4 is climbing a mountain. For all x_4, if x_4 plays squash, then x_4 is a writer.
There is at least one x_4 for which if x_4 plays squash, then x_4 is climbing a mountain can be inferred via the existential transitivity rule.