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. James is writing a letter. Robert is a nurse.
Barbara is an astronaut and James is writing a letter can be inferred via the conjunction rule. Barbara is an astronaut and Robert is a nurse can be inferred via the conjunction rule. James is writing a letter and Barbara is an astronaut can be inferred via the conjunction rule. James is writing a letter and Robert is a nurse can be inferred via the conjunction rule. Robert is a nurse and Barbara is an astronaut can be inferred via the conjunction rule. Robert is a nurse and James is writing a letter can be inferred via the conjunction rule.