gap> arc:=ArcPresentation(PureCubicalKnot(6,1));
[ [ 5, 8 ], [ 4, 6 ], [ 3, 5 ], [ 2, 4 ], [ 1, 3 ], [ 2, 7 ], [ 6, 8 ], [ 1, 7 ] ]
gap> cross:=[0,0,1,-1,-1,0];;
gap> cols:=[1,4,3];;
gap> ViewColouredArcDiagram(arc,cross,cols);  
convert-im6.q16: pixels are not authentic `/tmp/HAPtmpImage.txt' @ error/cache.c/QueueAuthenticPixelCacheNexus/4381.

