What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? For all z, z will climb a mountain if and only if z is a bartender. If Joseph were a bartender, then Elisabeth is writing a letter. Thomas is a politician if and only if Elisabeth is writing a letter. Thomas is not a politician.
If Thomas were a politician, then Elisabeth is writing a letter. If Elisabeth writes a letter, then Thomas is a politician. Elisabeth is not writing a letter. For all z, if z climbs a mountain, then z is a bartender. For all z, if z were a bartender, then z is climbing a mountain.