The right side shows a solution to the producer-consumer problem with $n$ buffers using three semaphores, where empty=n, mutex=1, and full=0 at the initial state. Some variables are missing in the consumer program. What are they?

The structure of the consumer process:

do {
    wait(V1);
    wait(V2);
    // remove an item

    signal(___);
    signal(___);
    // consume the item
} while (TRUE);

The structure of the producer process:

do {
    // produce an item in nextp

    wait(empty);
    wait(mutex);

    // add nextp to buffer

    signal(mutex);
    signal(full);
} while (TRUE);