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_7, x_7 will listen to a song or x_7 is an electrician. For all x_7, x_7 is an electrician if and only if x_7 is a nurse. There is at least one x_7 for which x_7 is a sailor. For all x_7, if x_7 listens to a song, then x_7 is a nurse.
For all x_7, if x_7 were an electrician, then x_7 is a nurse can be inferred via the universal biconditional elimination rule. For all x_7, if x_7 were a nurse, then x_7 is an electrician can be inferred via the universal biconditional elimination rule.