The list extremal number f(G)is defined for a graph G as the smallest integer k such that the join of G with a stable set of size k is not |V(G)|-choosable. In this paper,we find the exact value of f(G),where G is the union of edge-disjoint cycles of length three,four,five and six.Our results confirm two conjectures posed by S.Gravier,F.Maffray and B.Mohar.
