Toggle(move) current window between page 0 and page 1

Configuration
4

Hi Thomas,
your solution is better, it works :

    DestroyFunc TogglePage
    AddToFunc   TogglePage
    + I PipeRead `echo MoveToPage 0 $((1 - $[page.ny]))`

but why this version does not work? what is wrong with this one? I just want to understand more of FVWM funcations. (my FVWM only has 2 desks, each desk has 2 pages .)

 DestroyFunc TogglePagev2
 AddToFunc   TogglePagev2
 + I PipeRead `if [ $[page.ny]=0 ]; then echo MoveToPage 1 0; else echo  MoveToPage 0 0;`