What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? For all x_9, if x_9 writes a letter, then x_9 is making tea. For all x, x will write a letter. For all x_9, if x_9 makes tea, then x_9 is writing a letter.
For all x_9, x_9 will write a letter if and only if x_9 will make tea. For all x_9, x_9 will make tea if and only if x_9 will write a letter.