A black pawn at b5 can replace the black bishop c8 (the WK can be at h7 or h1 also). Obviously the composer prefers a non capturing white move. I think most composers do not mind the additional technical black piece!!

Exactly!

this is really nice. the position is open, the strategy is impeccable and the twinning mechanism is ingenious, and I'm sure it was a nightmare to get right with all the white force present-well done Vitaly!

This problem is theoretically interesting although it can't be expected that many people would care to clarify their own views of chess composition. What are the genuine features of some chess position and what are merely ornamental (visual) effects? Or, what is redundant in the idea and which pieces are redundant in the mechanism which translates the idea to a play?
(According to one's personal taste, a particular ornament could improve/spoil the appearance of someone/something. But the ornaments can't change the genuine content.)
The following analysis and comments tend only to draw attention to these questions, without the intention to evaluate particular composition(s).

bBa5 and bRf8 determine the square where bS will be pinned but actually they only prevent the same move 1.Sd4, each in one respective phase and each of them is redundant in the other respective phase, except for the other cooks. There is no reciprocity between bB/bR and they are mainly there for the soundness. If we accept that they are thematic, because they add to the thematic unity of the idea, then the unity of thematic mechanism is spoiled. Thematic unity of the idea is not realized through the adequate unity of mechanism.

This is my reply on comment #6. As it was mentioned by Nikola Quote:

chess composition is the art of chess pieces on the chessboard

, so the work of art should be graceful and subtle. On my glance, a capture of a chess-man (moreover, a non-thematic capture) is a crudeness that should be avoided in composing, if it is possible.

Vitaly, if you like it, it can be published as our joint problem, but also just as a version without mentioning my name (because I didn't upgrade the essence of your idea). There is a better equivalence/unity of the idea and the mechanism which represents it on the board (with reciprocity of bR/bQ), but that is only a rational view. I have to admit that despite that "rational elegance", I still see more "visual" beauty and elegance in your original. It's not easy to choose between the two kinds of beauty, beauty of logic and beauty of appearance. What I wished to emphasize is that a critic should be aware of both, before deciding which one is more important/convincing in each particular case.

Pieces of a mechanism are most precious. Merely technical pieces are much cheaper and also it's better to keep them out of thematic play. So, I also prefere bBc8 to Seetharaman's bPb5

OK Vitaly, thanks, I agree, whatever you decide! Although there's absolutely no true reason to put my name first. That would be an "ornamental" honour