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_8, x_8 will write a letter if and only if x_8 is a police officer. For all x_8, x_8 will not play squash. For all x_8, x_8 will write a letter if and only if x_8 will play squash.
For all x_8, if x_8 writes a letter, then x_8 is a police officer can be inferred via the universal biconditional elimination rule. For all x_8, if x_8 writes a letter, then x_8 is playing squash can be inferred via the universal biconditional elimination rule. For all x_8, if x_8 were a police officer, then x_8 is writing a letter can be inferred via the universal biconditional elimination rule. For all x_8, if x_8 plays squash, then x_8 is writing a letter can be inferred via the universal biconditional elimination rule. For all x_8, x_8 will not write a letter can be inferred via the universal biconditional elimination rule.