overAddBW1 (BW1 x1 y1) (BW1 x2 y2) = (BW1 s $ t + cs, c)
  where 
    (s, cs) = overAddWord x1 x2
    (t0, ct0) = overAddWord y1 y2
    (t, ct) = overAddWord t0 cs    
    c = ct + ct0
overAddBW1 (BW1 x1 y1) (BW1 x2 y2) = (BW1 s $ t + cs, c)
  where 
    (s, cs) = overAddWord x1 x2
    (t0, ct0) = overAddWord y1 y2
    (t, ct) = overAddWord t0 cs    
    c = ct + ct0
overAddBW1 (BW1 x1 y1) (BW1 x2 y2) = (BW1 s $ t + cs, c)
  where 
    (s, cs) = overAddWord x1 x2
    (t0, ct0) = overAddWord y1 y2
    (t, ct) = overAddWord t0 cs    
    c = ct + ct0