Dual pane toggle but with right = left

I'd like a button with a similar behavior than the command
Set Dual=Toggle
But , when I enable dual view, I want the right pane to point folder to point to the same folder as the left.

I've also written a button with the command
this one copy the left panel on the right, but when I reclick on it,
I do not switch to single view.

So instead of having two buttons , I'd like to have a single button,
which allows to switch between single and dual view, while keeping part right
the same as the left, when enabling dual.


Do you always want this to happen? If so then you just need to turn on Prefs - Layout - Default Folders: Same folder as primary file display.

Thanks for this solution.
If there's any other solution, that doesn't rely on that default setting, I may prefer it ; but I'm happy, with this one anyway.