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 Elisabeth were rich, then Charles is an astronaut. It is late or Barbara is not reading a book. If Charles were an astronaut, then Elisabeth is rich. If it is late, then Elisabeth is rich.
If it is late, then Charles is an astronaut can be inferred via the transitivity rule. If Barbara reads a book, then it is late can be inferred via the rewriting rule. Elisabeth is rich if and only if Charles is an astronaut can be inferred via the biconditional introduction rule. Charles is an astronaut if and only if Elisabeth is rich can be inferred via the biconditional introduction rule.