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: If David were a bartender, then Barbara is a mechanic. If David were a bartender, then Barbara is a mechanic. If Barbara were a mechanic, then David is a bartender.
David is a bartender if and only if Barbara is a mechanic can be inferred via the biconditional introduction rule. David is a bartender if and only if Barbara is a mechanic can be inferred via the biconditional introduction rule. Barbara is a mechanic if and only if David is a bartender can be inferred via the biconditional introduction rule. Barbara is a mechanic if and only if David is a bartender can be inferred via the biconditional introduction rule.