Statistical co-@C01434@ of different @C01286@ which may either belong to the same @C01335@ chains (@C01335@ isomorphism) or originate from different @H02854@ chains (@H02854@ isomorphism). Isomorphism is a general term: in the strict sense, the crystal structure is essentially the same throughout the range of compositions; in isodimorphism or isopolymorphism, there are two or more crystal structures, respectively, depending on composition.