dx/dt = 1 - x - y
dy/dt = x - y2
i) Find and plot equilibrium points and nullclines for system.
ii) Illustrate direction of vector field between nullclines.
iii) Draw some solution curves starting near, but not on, equilibrium point(s).
iv) Label every equilibrium as stable or unstable depending on behavior of solutions which begin nearby, and explain long-term behavior of all solutions.