N:=5;
A1:=REF(H,N)=HHV(H,2*N+1);
B1:=FILTER(A1,N);
C1:=BACKSET(B1,N+1);
HD:=FILTER(C1,N);
A2:=REF(L,N)=LLV(L,2*N+1);
B2:=FILTER(A2,N);
C2:=BACKSET(B2,N+1);
LD:=FILTER(C2,N);
DRAWLINE(LD,L,HD,H,0),COLORWHITE,LINETHICK2;
DRAWLINE(HD,H,LD,L,0),COLORWHITE,LINETHICK2;
