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 Mary works, then Richard is fast. Richard is fast if and only if it is raining. It is sunny or Elisabeth is not climbing a mountain. If it rains, then Elisabeth is climbing a mountain.
If Elisabeth climbs a mountain, then it is sunny can be inferred via the rewriting rule. If Richard were fast, then it is raining can be inferred via the biconditional elimination rule. If it rains, then Richard is fast can be inferred via the biconditional elimination rule.