The paper by Copeland, Liddle, and Wands presents a phase-plane analysis of cosmologies containing a barotropic fluid and a scalar field with an exponential potential. The authors investigate the evolution of these models in a spatially flat Friedmann-Robertson-Walker (FRW) universe. They find that for certain parameter ranges, there exist scaling solutions where the scalar field energy density tracks that of the barotropic fluid, leading to a late-time attractor solution. These solutions are stable and unique when they exist. However, fluid-dominated solutions are always unstable, except for the cosmological constant case ($\gamma = 0$). The relative energy density of the fluid and scalar field depends on the steepness of the exponential potential, which is constrained by nucleosynthesis to $\lambda^2 > 20$. The paper also discusses the implications of these findings for the relic density problem, showing that standard inflation models cannot significantly reduce the initial density of the exponential potential, thus failing to alleviate the relic density problem. The authors conclude that only inflation models with effectively constant energy density and an exponentially large number of e-foldings, such as some models of hybrid inflation, could potentially weaken the bound on $\lambda^2$.The paper by Copeland, Liddle, and Wands presents a phase-plane analysis of cosmologies containing a barotropic fluid and a scalar field with an exponential potential. The authors investigate the evolution of these models in a spatially flat Friedmann-Robertson-Walker (FRW) universe. They find that for certain parameter ranges, there exist scaling solutions where the scalar field energy density tracks that of the barotropic fluid, leading to a late-time attractor solution. These solutions are stable and unique when they exist. However, fluid-dominated solutions are always unstable, except for the cosmological constant case ($\gamma = 0$). The relative energy density of the fluid and scalar field depends on the steepness of the exponential potential, which is constrained by nucleosynthesis to $\lambda^2 > 20$. The paper also discusses the implications of these findings for the relic density problem, showing that standard inflation models cannot significantly reduce the initial density of the exponential potential, thus failing to alleviate the relic density problem. The authors conclude that only inflation models with effectively constant energy density and an exponentially large number of e-foldings, such as some models of hybrid inflation, could potentially weaken the bound on $\lambda^2$.