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1992_01_01_erdos_fon_der_flaass_kostochka_tuza: Erdős, Fon-Der-Flaass, Kostochka and Tuza (1992) prove f(k,3)=2k, f(k,4)=ceil(3k/2), f(k,5)=ceil(5k/4) and f(k,6)=k, so the constants c_r of the second question exist for r from 3 to 6.
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