What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? William is writing a letter or Linda is a musician. If Linda were a musician, then John is happy. For all y, y is a writer if and only if y will write a letter. If William were a writer, then John is happy.
For all y, if y were a writer, then y is writing a letter. For all y, if y writes a letter, then y is a writer.