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 Charles is reading a book. Charles is not reading a book. It is overcast or Susan is not playing a game.
If Susan plays a game, then it is overcast can be inferred via the rewriting rule. If it is overcast, then Charles is reading a book can be inferred via the biconditional elimination rule. If Charles reads a book, then it is overcast can be inferred via the biconditional elimination rule. It is not overcast can be inferred via the biconditional elimination rule.