public void terminated(Pipe pipe_) {
        //  Remove the pipe from the list; adjust number of matching, active and/or
        //  eligible pipes accordingly.
        if (pipes.indexOf (pipe_) < matching)
            matching--;
        if (pipes.indexOf (pipe_) < active)
            active--;
        if (pipes.indexOf (pipe_) < eligible)
            eligible--;
        pipes.remove(pipe_);
    }