As a consequence of an early result of Pach we show that every maximal triangle-free graph is either homomorphic with a member of a speciic innnite sequence of 3-colourable graphs or it contains the Petersen graph minus one vertex as a subgraph. From this result and further structural observations we derive that if a (not necessarily maximal) triangle-free graph of order n has minimum degree n=...

A graph is prismatic if for every triangle T , every vertex not in T has exactly one neighbour in T . In a previous paper we gave a complete description of all 3-colourable prismatic graphs, and of a slightly more general class, the “orientable” prismatic graphs. In this paper we describe the non-orientable ones, thereby completing a description of all prismatic graphs. Since complements of pri...