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: John is not a taxi driver. Barbara is fast if and only if John is a taxi driver. Barbara is fast if and only if it is late.
If Barbara were fast, then John is a taxi driver can be inferred via the biconditional elimination rule. If Barbara were fast, then it is late can be inferred via the biconditional elimination rule. If John were a taxi driver, then Barbara is fast can be inferred via the biconditional elimination rule. If it is late, then Barbara is fast can be inferred via the biconditional elimination rule. Barbara is not fast can be inferred via the biconditional elimination rule.