What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Joseph is not happy. Robert is a scientist if and only if Charles is writing a letter. If Robert were a scientist, then it is raining. If it rains, then Joseph is happy.
It is not raining. If Robert were a scientist, then Charles is writing a letter. If Charles writes a letter, then Robert is a scientist.