What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? For all y, if y were sad, then y is a doctor. For all y, if y were a doctor, then y is sad. For all y, if y were a doctor, then y is sad.
For all y, y is sad if and only if y is a doctor. For all y, y is sad if and only if y is a doctor. For all y, y is a doctor if and only if y is sad. For all y, y is a doctor if and only if y is sad.