\\ Universal elliptic curve over X(4,4) e44 = ellinit([0,-1-(t^2-1)^2/(t^2+1)^2,0,(t^2-1)^2/(t^2+1)^2,0]) P44= [ (t^2-1)/(t^2+1), 2*I*(t^2-1)/(t^2+1)^2] Q44 = [ (t-1)^2/(t^2+1), 2*t*(t-1)^2/(t^2+1)^2 ] ellisoncurve(e44,P44) ellisoncurve(e44,Q44) \\ Universal elliptic curve over X(4,2) e42 = ellinit([0,-1-s^2,0,s^2,0]) P42 = [s, I*s*(1-s)] a1 = [0,0]; a2=[1,0]; a3 = [s^2,0]; P42 elladd(e42,P42,a1) elladd(e42,P42,a2) elladd(e42,P42,a3) g = elladd(e42,[x,y],[x,y]) g = g[1]-P42[1] g = substpol(g,y^2,x*(x-1)*(x-s^2)) g = numerator(g) substpol(g/x^2,x+s^2/x,u)