Special subdivisions ofK 4 and 4-chromatic graphs

In this paper we consider special subdivisions ofK ₄ in which some of the edges are left undivided. A best possible extremal-result for the case where the edges of a Hamiltonian path are left undivided is obtained. Moreover special subdivisions as subgraphs of 4-chromatic graphs are studied. Our main-result on 4-chromatic graphs says that any 4-critical graphG contains an odd cycleC without diagonals such thatG-V (C) is connected.