CoCalc -- 4-1;1

GAP 4.8.9 installation with standard packages -- copy to your CoCalc project to get it

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#1

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1 0 0 0 0
1 1 0 0 0
0 -1 1 0 0
0 0 -1 1 1
0 0 0 -1 1

dim5/4-1;1a