ellipse (a:RR,b:RR,C:Point )=ellipse(a,b,C,[1,0])

ellipse (a:RR,b:RR,v:Vector )=ellipse(a,b,point(0,0),v)

ellipse (a:RR,b:RR)=ellipse(a,b,point(0,0),[1,0])

ellipse (a:RR,b:RR,C:Point,v:Vector )

ellipse (a:RR,b:RR,C:Point,α:RR)=ellipse(a,b,C,[cos(α),sin(α)])