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: If Elisabeth were an office clerk, then it is overcast. If John were happy, then Barbara is playing squash. Elisabeth is an office clerk or Barbara is not playing squash. If it is overcast, then John is happy.
If Elisabeth were an office clerk, then John is happy can be inferred via the transitivity rule. If it is overcast, then Barbara is playing squash can be inferred via the transitivity rule. If Barbara plays squash, then Elisabeth is an office clerk can be inferred via the rewriting rule.