Forbidden subgraph pairs for traceability of block-chains

A block-chain is a graph whose block graph is a path, i.e. it is either a $P_1$, a $P_2$, or a 2-connected graph, or a graph of connectivity 1 with exactly two end-blocks. A graph is called traceable if it contains a Hamilton path. A traceable graph is clearly a block-chain, but the reverse does not hold in general. In this paper we characterize all pairs of connected graphs ${R,S}$ such that every ${R,S}$-free block-chain is traceable.