Did you look at the ExRem command: 
buy = ExRem( buy, sell );
sell = ExRem( sell, buy ); 
which helps ignore multiple signals.
You might also look at the Flip command.  
--- In amibroker@xxxxxxxxx ps.com, "ics4mer" <ics4mer@xxx > wrote:
>
> Hi,
> 
> Looking for some help with following situation.
> 
> Say we have 3 moving averages:
> 
> MA_Short = MA(C,20)
> MA_Med = MA(C,100)
> MA_long = MA(C,200);
> 
> My signals are the following
> 
> Buy  = MA_Med > MA_Long AND Cross(MA_Short, MA_Med);
> Sell = Cross(MA_Med, MA_Short);
> 
> However, I only want to trade the first occurence of cross(MA_short, MA_Med).
> 
> I don't want to take another long trade until MA_Med has dipped below MA_Long and risen above MA_Long again and the Cross(short, med) situation occurs again.
> 
> I suspect it has something to do with the flip() function but I can't quite sus it out!
> 
> I've nearly worked it out with a loop, but I'm sure that it's not the correct way to use AFL.
> 
> Any help greatly appreciated!
> 
> TIA
> 
> Robert
>