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: It is overcast if and only if William is taking a plane. For all x_10, x_10 will not listen to a song. It is overcast if and only if Elisabeth is listening to a song.
If it is overcast, then William is taking a plane can be inferred via the biconditional elimination rule. If it is overcast, then Elisabeth is listening to a song can be inferred via the biconditional elimination rule. If William takes a plane, then it is overcast can be inferred via the biconditional elimination rule. If Elisabeth listens to a song, then it is overcast can be inferred via the biconditional elimination rule.