I thought I had reasoned that the add_patch would only happen when the patch was not already in a cell, but I missed reasoning about merged cells. So switched to a set 'add' instead of 'add_new'.
I thought I had reasoned that the add_patch would only happen when the patch was not already in a cell, but I missed reasoning about merged cells. So switched to a set 'add' instead of 'add_new'.