What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? William is not writing a letter. If William plays squash, then Linda is an artist. If William plays squash, then William is writing a letter. If Linda were an artist, then William is playing squash.
William is not playing squash. If Linda were an artist, then William is writing a letter. William is playing squash if and only if Linda is an artist. Linda is an artist if and only if William is playing squash.