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: Barbara is fast if and only if it is snowing. Patricia is not playing squash. Joseph is writing a letter if and only if it is not snowing. Joseph is not writing a letter. If Barbara were fast, then Patricia is playing squash.
Since the premises are contradictory, we can infer anything from them.