What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? For all x_15, x_15 will not climb a mountain. For all x_15, if x_15 works, then x_15 is climbing a mountain. Susan is sad if and only if Thomas is working.
If Susan were sad, then Thomas is working. If Thomas works, then Susan is sad. For all x_15, x_15 will not work.