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 x for which x is not happy. For all x, if x were happy, then x is writing a letter. For all x, x is happy or x will not write a letter.
For all x, if x writes a letter, then x is happy can be inferred via the universal rewriting rule.