where i'm wrong
 

> with(plottools);
> with(plots);
> m := PLOT(polygon([[2, 2], [2, 3], [4, 3], [4, 2]], color = blue), polygon([[1, 1], [1, 4], [5, 4], [5, 1]], color = red), polygon([[1, 4], [3, 6], [5, 4]], thickness = 3, color = red), curve([[4.5, 5.5], [5, 6]]), polygon([[3.5, 5], [4, 5.5], [4.5, 5], [4, 4.5]], color = red));
> n := PLOT(polygon([[2, 2], [2, 3], [4, 3], [4, 2]], color = green), polygon([[1, 1], [1, 4], [5, 4], [5, 1]], color = red), polygon([[1, 4], [3, 6], [5, 4]], thickness = 3, color = red), curve([[5.5, 6], [6, 6.5]]), polygon([[3.5, 5], [4, 5.5], [4.5, 5], [4, 4.5]], color = red));
> display([m, n], insequence = true);
Error, (in plots:-display) expecting plot structures but received: [m, n]
>