difficulties

difficalty to define strands start and end residuesd1nfde2(see two strands as one or devide into two sheets/domains or delete that strand)

difficalty to decide if a strand should be delete/add or not.1g4m1cf1(how many residues are long enough/ short enough to be add/delete?)(any other way to determin a strand should be add/delete?)

difficalty to define two main sheets1edq (how twisted should be ignored?)(how large/ how small a sheet should be)

difficalty to define a domain1h6e (you can cut both ways)

difficalty to choose two sheets1h6e(if we have more then two sheets, should we delete a sheets or should we devide into two domains?)

there's always something in betweenso, we choose to modify as few as possible while have some consistency.