Question: Mistake when drawing a few figures, how to fix

restart;
with(plots);
with(plottools);
k := disk([0, 0], 3, color = white)

k1 := polygon([[0, 0], [3, 4], [3, 1]])
display({k, k1});
Error, (in plots:-display) expecting plot structures but received: {k1}
 

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