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_16, x_16 is an astronaut or x_16 is not sad. For all x_16, if x_16 were an astronaut, then x_16 is a police officer. There is at least one x_16 for which x_16 is sad. For all x_16, if x_16 were a police officer, then x_16 is an astronaut.
For all x_16, if x_16 were sad, then x_16 is an astronaut can be inferred via the universal rewriting rule. For all x_16, x_16 is an astronaut if and only if x_16 is a police officer can be inferred via the universal biconditional introduction rule. For all x_16, x_16 is a police officer if and only if x_16 is an astronaut can be inferred via the universal biconditional introduction rule.