More on 2-chains with 1-shell boundaries in rosy theories

摘要

In [4], B. Kim, and the authors classified 2-chains with 1-shell boundaries into either RN (renamable)-type or NR (non renamable)-type 2-chains up to renamability of support of subsummands of a 2-chain and introduced the notion of chain-walk, which was motivated from graph theory : a directed walk in a directed graph is a sequence of edges with compatible condition on initial and terminal vertices between sequential edges. We consider a directed graph whose vertices are 1-simplices whose supports contain 0 and edges are plus/minus of 2-simplices whose supports contain 0. A chain-walk is a 2-chain induced from a directed walk in this graph. We reduced any 2-chains with 1-shell boundaries into chain-walks having the same boundaries. In this paper, we reduce any 2-chains of 1-shell boundaries into chain-walks of the same boundary with support of size 3. Using this reduction, we give a combinatorial criterion determining whether a minimal 2-chain is of RN-or NR-type. For a minimal RN-type 2-chains, we show that it is equivalent to a 2-chain of Lascar type (coming from model theory) if and only if it is equivalent to a planar type 2-chain.