f:=sqrt( 1+4*cos(sqrt(3)*X/2)*cos(Y/2) + 4*(cos(Y/2))**2): a:=2*Pi/sqrt(3): b:=1/sqrt(3): c:=4*Pi/3: plot3d({-f,f}, X=-a..a,Y=-c+b*abs(X)..c-b*abs(X), style=PATCH,scaling=CONSTRAINED);