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import three; size(100); path3 g=(1,0,0)..(0,1,0)..(-1,0,0)..(0,-1,0)..cycle; draw(g); draw(O--Z,red+dashed,Arrow3); draw(((-1,-1,0)--(1,-1,0)--(1,1,0)--(-1,1,0)--cycle)); dot(g,red);