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: For all x_11, x_11 is happy or x_11 will play tennis. For all x_11, if x_11 were happy, then x_11 is a lawyer. For all x_11, if x_11 were a lawyer, then x_11 is sad. For all x_11, x_11 will play tennis if and only if x_11 is a lawyer. There is at least one x_11 for which x_11 is a musician.
For all x_11, if x_11 were happy, then x_11 is sad can be inferred via the universal transitivity rule. For all x_11, if x_11 plays tennis, then x_11 is a lawyer can be inferred via the universal biconditional elimination rule. For all x_11, if x_11 were a lawyer, then x_11 is playing tennis can be inferred via the universal biconditional elimination rule.