Another weird and wonderful Czech patent. This one appears to be for a variant of the Favorit Special that would have incorporated a second cable used to control the chain tension, in the style of various French derailleurs of the 1950s like the Simplex Juy 51, Simplex Juy 543 or Huret Louison Bobet models.
By 1972 it was well accepted that there was precisely no engineering case for a second cable, or even for any direct control over chain tension. However ZZR in Poland continued to proudly produce a copy of the Simplex Juy 51, and it is possible that this patent relates to a design that was for Polish consumption. In the mid 1970s Romet (ZZR’s new name) did adopt the standard, single cable, Favorit Special as its default derailleur.