What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? If Charles plays squash, then Thomas is writing a letter. If Thomas writes a letter, then Richard is playing tennis. For all z, if z plays tennis, then z is an artist. Richard is not an artist. If Thomas writes a letter, then Charles is playing squash.
If Charles plays squash, then Richard is playing tennis. Charles is playing squash if and only if Thomas is writing a letter. Thomas is writing a letter if and only if Charles is playing squash.