eqBox (Unfold _ t (x, u), s) (Unfold _ t' (x', u'), s') =
    do eqBox (t,s) (t',s')
       eq (x,Boxed (u,s)) (x',Boxed (u',s'))
eqBox (Unfold _ t (x, u), s) (Unfold _ t' (x', u'), s') =
    do eqBox (t,s) (t',s')
       eq (x,Boxed (u,s)) (x',Boxed (u',s'))
eqBox (Unfold _ t (x, u), s) (Unfold _ t' (x', u'), s') =
    do eqBox (t,s) (t',s')
       eq (x,Boxed (u,s)) (x',Boxed (u',s'))