What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? David is writing a letter or it is overcast. John is a poet if and only if Mary is a musician. For all x, x is not a musician. For all x_23, if x_23 writes a letter, then x_23 is rich. If it is overcast, then David is rich.
If John were a poet, then Mary is a musician. If Mary were a musician, then John is a poet.