The green pulleys are identical. The yellow pulleys are identical.
The blue cable with two fixed ends wraps round the green pulleys.
The black cable with two fixed ends wraps round the yellow pulleys.
Four vertical cable branches must be parallel.
The pink slider has vertical translational motion (with or without guideway).
Eccentric arrangement between the green pulleys and the yellow pulleys in vertical direction is possible.
This mechanism was used for drawing parallel horizotal straight lines.