> plot( [t*(t^2+1)/(t^4+1), -t*(t^2-1)/(t^4+1), t=-10..10]);

> plot( [t*(t^2+1)/(t^4+1), -t*(t^2-1)/(t^4+1), t=-10..infinity]);

> plot( [t*(t^2+1)/(t^4+1), -t*(t^2-1)/(t^4+1), t=-infinity..10]);

> lem1:=plot([cos(2*t), t, t=-Pi/4..Pi/4], coords=polar):

> lem2:=plot([-cos(2*t), t, t=-Pi/4..Pi/4], coords=polar):

> with(plots):

> display([lem1, lem2]);

>