i=i-(chain_end[c]-chain_start[c])-3
ssbond=[ [e[0]-unres_shift[c[0]]+1,e[1]-unres_shift[c[1]]+1] for e,c in zip(ssbond,ssbond_ch)]
i=i-(chain_end[c]-chain_start[c])-3
ssbond=[ [e[0]-unres_shift[c[0]]+1,e[1]-unres_shift[c[1]]+1] for e,c in zip(ssbond,ssbond_ch)]