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In this paper we study some open questions related to the smallest order f (C, ¬H) of a 4-regular graph which has a connectivity property C but does not have a hamiltonian property H. In particular, C is either connectivity, 2-connectivity or 1-toughness and H is hamiltonicity, homogeneous traceability or traceability. A standard theoretical approach to these questions had already been used in the literature, but in many cases did not succeed in determining the exact value of f (). Here we have chosen to use Integer Linear Programming and to encode the graphs that we are looking for as the binary solutions to a suitable set of linear inequalities. This way, there would exist a graph of order n with certain properties if and only if the corresponding ILP had a feasible solution, which we have determined through a branch-and-cut procedure. By using our approach, we have been able to compute f (C, ¬H) for all the pairs of considered properties with the exception of C =1-toughness, H =traceability. Even in this last case, we have nonetheless significantly reduced the interval [LB, U B] in which f (C, ¬H) was known to lie. Finally, we have shown that for each n ≥ f (C, ¬H) (n ≥ U B in the last case) there exists a 4-regular graph on n vertices which has property C but not property H.
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