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_6, x_6 is happy or x_6 is an office clerk. For all x_6, x_6 is a sailor or x_6 is not an office clerk. For all x_6, x_6 is a cashier. For all x_6, if x_6 were happy, then x_6 is a sailor.
For all x_6, if x_6 were an office clerk, then x_6 is a sailor can be inferred via the universal rewriting rule.