What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Elisabeth is happy if and only if Jessica is writing a letter. Barbara is a scientist if and only if Jessica is writing a letter.
If Elisabeth were happy, then Jessica is writing a letter. If Barbara were a scientist, then Jessica is writing a letter. If Jessica writes a letter, then Elisabeth is happy. If Jessica writes a letter, then Barbara is a scientist.