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_10, if x_10 writes a letter, then x_10 is playing squash. If Patricia were a writer, then Barbara is writing a letter. If Barbara plays squash, then Patricia is a writer.
If Barbara plays squash, then Barbara is writing a letter can be inferred via the transitivity rule.