Chapter 2: Basic Abstract Data Types. Problem 2.9

The following procedure was intended to remove all occurances of element x from list L. Explain why it doesn't always work and suggest a way to repair the procedure so it performs its intended task. 

procedure delete (x : elementtype; var L: LIST); 
    var
        p: position
    begin
        p := FIRST(L);
        while p <> END(L) do begin
            if RETRIEVE(p,L) = x then
                DELETE(p,L);
        p := NEXT(p,L);
    end
end; {delete}

In the above problem, you can't just delete the NODE without adjusting the previous pointer to point to the node after the one to be deleted.