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 take a plane if and only if x_7 will work. For all x_7, if x_7 were a doctor, then x_7 is working. For all x_7, x_7 will not take a plane. There is at least one x_7 for which x_7 is a doctor or x_7 is a sailor.
For all x_7, if x_7 takes a plane, then x_7 is working can be inferred via the universal biconditional elimination rule. For all x_7, if x_7 works, then x_7 is taking a plane can be inferred via the universal biconditional elimination rule. For all x_7, x_7 will not work can be inferred via the universal biconditional elimination rule.