I'm trying to plot this equation with initial conditions. I'm following the exact same code that my professor used, but it isn't working. 

restart; with(plots): with(DEtools):

DE := y(t)^2*(4-y(t)^2);

p1 := DEplot( DE, y(t), t=0..1/2, {[y(0)=1],[y(0)=3]}, arrows=none, thickness=2, linecolor=[blue,green]):

Under the last line of code I get the error "Error, (in DEtools/DEplot/CheckInitial) the 'number' option...