[amibroker] Variable Call back in formula - help

["hotdayinlimbo" <dj@xxxxxxxx>]

Hi - Somewhat of newbie coming over from CQG. 

I am trying to duplicate this coding from CQG and getting stuck 
here: 
CQG 
yy1:= if(xx1 > yy1[-1], low, high); 
AMIBroker 
yy1=iif(xx1 > ref(yy1,-1), low, high); 

I cannot get Amibroker to recognize ref(yy1,-1)... is there another 
way to reference the variable one ago in the same line of code? 

Thx, 
DJ




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