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_14 for which x_14 is an astronaut or x_14 is not a mechanic. For all x_14, x_14 is a mechanic if and only if x_14 is a nurse. For all x_14, x_14 is not an astronaut.
There is at least one x_14 for which if x_14 were a mechanic, then x_14 is an astronaut can be inferred via the existential rewriting rule. For all x_14, if x_14 were a mechanic, then x_14 is a nurse can be inferred via the universal biconditional elimination rule. For all x_14, if x_14 were a nurse, then x_14 is a mechanic can be inferred via the universal biconditional elimination rule.