What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? For all y_4, if y_4 were a mechanic, then y_4 is writing a letter. For all y_4, if y_4 were excited, then y_4 is writing a letter. For all y_4, y_4 is excited or y_4 is a mechanic. For all y_4, if y_4 writes a letter, then y_4 is a mechanic.
For all y_4, if y_4 were excited, then y_4 is a mechanic. For all y_4, y_4 will write a letter. For all y_4, y_4 is a mechanic if and only if y_4 will write a letter. For all y_4, y_4 will write a letter if and only if y_4 is a mechanic.