Model5=ContourPlot[x^4+2 x^3+ 2 x^2 y^2+ 2 x y^2+y^4-y^2-y/2==0,{x,-3,1},{y,-2,2}]

Model6=ContourPlot[(x^4)/4+x^3+(x^2 y^2)/2+x y^2+y^4/4-y^2-4y==0,{x,-5,2},{y,-2,5}]

Model7=ContourPlot[(Sqrt[(1-x^2)]+1/(10+100x^2)-y)(Sqrt[(1-x^2)]-6/(10+100 x^2)+y)==0,{x,-2,2},{y,-2,2}]

Model8=ContourPlot[9x^4+12x^3+12x^2 y^2+8x y^2+4y^4-4y^2-16y==0,{x,-2,2},{y,-1,3}]