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: William is taking a plane or Jessica is climbing a mountain. James is writing a letter if and only if William is taking a plane. James is writing a letter or Jessica is not climbing a mountain.
If Jessica climbs a mountain, then James is writing a letter can be inferred via the rewriting rule. If James writes a letter, then William is taking a plane can be inferred via the biconditional elimination rule. If William takes a plane, then James is writing a letter can be inferred via the biconditional elimination rule.