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: John is not climbing a mountain. It is late or John is not climbing a mountain. John is climbing a mountain if and only if it is late.
If John climbs a mountain, then it is late can be inferred via the rewriting rule. If John climbs a mountain, then it is late can be inferred via the biconditional elimination rule. If it is late, then John is climbing a mountain can be inferred via the biconditional elimination rule. It is not late can be inferred via the biconditional elimination rule.