局部低点预选a:=backset(llv(l,5)<ref(llv(l,4),1),4);局部低点预选b:=backset(局部低点预选a=0 and ref(局部低点预选a,1)=1,2);局部低点预选c:=if(局部低点预选b=1 and ref(局部低点预选b,1)=0,-1,0);aaaa:局部低点预选c=-1;(backset为未来函数,请谨慎)
a:=if(c<ref(o,1) and c<o,1,0);p1:=a;b:=if(c<ref(o,2) and c<o,1,0);p2:=b;stickline(p1=0 and ref(p1,1)=1 and p2=0 and ref(p2,1)=1,open,close,3,0),colormagenta;