load(draw);
draw2d(
    terminal= svg,
    xlabel  = "X",
    ylabel  = "Z",
    yrange  = [0,10],
    grid    = true,
    axis_top= false,
    axis_right=false,
    dimensions  = 100*[4,3.5],
    file_name   = "3D curve",
    line_width  = 2,
    color   = black,
    explicit(3*x,x,0,2.5),
    color   = red,
    explicit(x^2+x+1,x,-2.5,2.5)
);