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 y for which y is a mechanic or y is a police officer. For all y, y is an astronaut or y is not a police officer. For all y, y is a mechanic if and only if y is an astronaut.
For all y, if y were a police officer, then y is an astronaut can be inferred via the universal rewriting rule. For all y, if y were a mechanic, then y is an astronaut can be inferred via the universal biconditional elimination rule. For all y, if y were an astronaut, then y is a mechanic can be inferred via the universal biconditional elimination rule.