answered 8 years ago
What about this?
var('y') R = region_plot( abs(x) < 1 - abs(y) / 3, (x,-4,4), (y,-4,4), plot_points=300) S = region_plot( abs(y) < 1 - abs(x) / 3, (x,-4,4), (y,-4,4), plot_points=300) (R+S).show(aspect_ratio=1)