The variable-slant-parallelogram of the 1987 Campagnolo Chorus is described in loving detail in this patent. Unsurprisingly, no mention is made of Boris Rostislavovich Mikhailov's curiously similar Soviet patent dating from 1979.
Browse associated derailleurs.
Campagnolo Chorus (C010-LG 1st style) 1987
Campagnolo Chorus (C010-SM 1st style) 1987
Campagnolo Chorus (C010-SM 3rd style) 1990?