What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Karen is writing a letter if and only if John is playing squash. Karen is writing a letter or Elisabeth is driving a car. It is overcast if and only if John is playing squash. It is not overcast.
If Karen writes a letter, then John is playing squash. If it is overcast, then John is playing squash. If John plays squash, then Karen is writing a letter. If John plays squash, then it is overcast. John is not playing squash.