Before revision:  Our results build on a recent work of Chou, Golovnev, Sudan,  and Velusamy who show tight  inapproximability results for some constraint satisfaction problems over arbitrary (finite) alphabets.
After revision:  Our results build on recent works of Chou, Golovnev, Sudan, and Velusamy who show tight inapproximability results for some constraint satisfaction problems over arbitrary (finite) alphabets.