randomizing within a fixed alternating pattern

[jarvis24]

I've been working on a nice simple notation system for creating constraints like that, but I haven't programmed it. Might be working by the next version. The only way I can think of to do this in v2006 would be to treat the BA's as BGR pairs and draw the stimuli randomly from stimlists as follows:

BGR WGR STIM
1   0   $A
2   0   $A
3   0   $A
4   0   $A
5   0   $A
6   0   $A
7   0   $B
7   0   $A
8   0   $B
8   0   $A