What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? If David climbs a mountain, then it is late. David is climbing a mountain if and only if Elisabeth is writing a letter. Elisabeth is writing a letter or Elisabeth is not a politician.
If Elisabeth were a politician, then Elisabeth is writing a letter. If David climbs a mountain, then Elisabeth is writing a letter. If Elisabeth writes a letter, then David is climbing a mountain.