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: Michael is not happy. Karen is playing tennis if and only if Jessica is cooking. If Karen plays tennis, then Michael is writing a letter. For all x_21, x_21 will write a letter if and only if x_21 is happy.
If Karen plays tennis, then Jessica is cooking can be inferred via the biconditional elimination rule. If Jessica cooks, then Karen is playing tennis can be inferred via the biconditional elimination rule. For all x_21, if x_21 writes a letter, then x_21 is happy can be inferred via the universal biconditional elimination rule. For all x_21, if x_21 were happy, then x_21 is writing a letter can be inferred via the universal biconditional elimination rule.