What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? If it is sunny, then Karen is writing a letter. If Thomas takes a plane, then it is sunny. If Thomas takes a plane, then it is sunny. Karen is writing a letter if and only if Thomas is taking a plane.
If Thomas takes a plane, then Karen is writing a letter. If Thomas takes a plane, then Karen is writing a letter. If Karen writes a letter, then Thomas is taking a plane. If Thomas takes a plane, then Karen is writing a letter.