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, if x_4 plays squash, then x_4 is a sailor. For all x_4, if x_4 were a sailor, then x_4 is a lawyer. For all x_4, if x_4 were a lawyer, then x_4 is playing squash. Barbara is not playing squash.
For all x_4, if x_4 plays squash, then x_4 is a lawyer can be inferred via the universal transitivity rule. For all x_4, if x_4 were a sailor, then x_4 is playing squash can be inferred via the universal transitivity rule. For all x_4, if x_4 were a lawyer, then x_4 is a sailor can be inferred via the universal transitivity rule.