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 working if and only if Karen is playing tennis. For all x_17, if x_17 writes a letter, then x_17 is playing tennis. Karen is writing a letter or Karen is not playing tennis. John is not working.
If Karen plays tennis, then Karen is writing a letter can be inferred via the rewriting rule. If John works, then Karen is playing tennis can be inferred via the biconditional elimination rule. If Karen plays tennis, then John is working can be inferred via the biconditional elimination rule. Karen is not playing tennis can be inferred via the biconditional elimination rule.