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 an astronaut or Robert is not writing a letter. If Barbara were an astronaut, then Sarah is a bartender. Robert is writing a letter or Sarah is not a bartender.
If Robert writes a letter, then Barbara is an astronaut can be inferred via the rewriting rule. If Sarah were a bartender, then Robert is writing a letter can be inferred via the rewriting rule.