  This paper studies the market viability with proportional transaction costs.
Instead of requiring the existence of strictly consistent price systems (SCPS)
as in the literature, we show that strictly consistent local martingale systems
(SCLMS) can successfully serve as the dual elements such that the market
viability can be verified. We introduce two weaker notions of no arbitrage
conditions on market models named no unbounded profit with bounded risk (NUPBR)
and no local arbitrage with bounded portfolios (NLABP). In particular, we show
that the NUPBR and NLABP conditions in the robust sense for the smaller bid-ask
spreads is the equivalent characterization of the existence of SCLMS for
general market models. We also discuss the implications for the utility
maximization problem.
