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 will write a letter if and only if x will sleep. For all x, if x writes a letter, then x is sleeping.
There is at least one x for which if x writes a letter, then x is sleeping can be inferred via the existential biconditional elimination rule. There is at least one x for which if x sleeps, then x is writing a letter can be inferred via the existential biconditional elimination rule.