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2019-06-05 16:03:06 +0200 asked a question chromatic polynomial graph with loops

Since there are no proper colorings of graphs with loops, their chromatic polynomial should be zero.

SageMath 8.6 however seems to ignore the loops and returns a nonzero chromatic polynomial for the graph on one vertex with one loop edge.

sage: Graph([[1, 1]], multiedges=True, loops=True).chromatic_polynomial()