Theory of ordered Banach spaces and related equations was rst introduced by M.G.Krein and M.A.Rutman in the 1940s. The theory was then developed and many signi cant results were achieved in the period of time from 1950 to 1980 in the works of M.A.Krasnoselskii and his students. Some notable names among them are E.N.Dancer, P.Rabinowitz, R.Nussbaum and W.V.Petryshyn. The theory has been developing until today with huge range of applications in di¤erential and integral equations, physics, chemistry, biology, control theory, optimization, medicine, economics, linguistics,.