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: There is at least one x_4 for which x_4 will read a book if and only if x_4 is an electrician. For all x_4, x_4 will not take a plane. For all x_4, x_4 will read a book if and only if x_4 will take a plane.
For all x_4, if x_4 reads a book, then x_4 is taking a plane can be inferred via the universal biconditional elimination rule. There is at least one x_4 for which if x_4 reads a book, then x_4 is an electrician can be inferred via the existential biconditional elimination rule. For all x_4, if x_4 takes a plane, then x_4 is reading a book can be inferred via the universal biconditional elimination rule. There is at least one x_4 for which if x_4 were an electrician, then x_4 is reading a book can be inferred via the existential biconditional elimination rule. For all x_4, x_4 will not read a book can be inferred via the universal biconditional elimination rule.