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_4, x_4 is a poet or x_4 is a mechanic. For all x_4, if x_4 were a mechanic, then x_4 is an electrician. There is at least one x_4 for which x_4 is a poet if and only if x_4 is an electrician.
There is at least one x_4 for which if x_4 were a poet, then x_4 is an electrician can be inferred via the existential biconditional elimination rule. There is at least one x_4 for which if x_4 were an electrician, then x_4 is a poet can be inferred via the existential biconditional elimination rule.