x(j);
        if(x1 > synthesis_xs[1] && x2 < synthesis_xs[2]){
            y1 = polynomial_in_x(X, x1, synthesis_n);
            y2 = polynomial_in_x(X, x2, synthesis_n);
            synthesis_context.moveTo(x_to_client(x1), y_to_client(y1));
            synthesis_context.lineTo(x_to_client(x2), y_to_client(y2));
        }
    }
    synthesis_context.strokeStyle="#661100";
    synthesis_context.stroke();
    synthesis_context.closePath();
    
    // grid
    draw_grid_on(synthesis_context);

    // dots
 