Simultaneous Parallel and Series Operation

One feature of driving 2 sides of a tractor independently is the possibility of driving the tracks in series or in parallel. How to achieve this?

In 2015, we have tried Bulldozer Hydraulics which used a double selector valve to achieve simulataneous parallel/series. This did not work because 2 valves downstream of one another always operate in series. This means that the only way a valve can operate in parallel is if it is a multiple port parallel valve (multiport series valve probably also exist). Left side has a 2 spool parallel cylinder valve (checks), and when the two spools are pressed, parallel reversible motion can occur. This is when each spool is connected to one side. Series operation occurs when the left spool is activated on the parallel valve for the left side - and a downstream series cylinder valve operates the right side.