(the github diff is rendering this funny )

it went from 
``EQ | size y0 == 1 -> hinted $ go11 (lo x0) (head x0) (lo y0) (head y0)
 ``

to 
``
 EQ | size y0 == 0 -> empty
EQ | size y0 == 1 -> hinted $ go11 (lo x0) (head x0) (lo y0) (head y0) ``

naively, that seems fine to me.