/**
   * Start building an instance which maps {@code x = x1} to {@code y = y1}. Both arguments must be
   * finite. Call either {@link LinearTransformationBuilder#and} or {@link
   * LinearTransformationBuilder#withSlope} on the returned object to finish building the instance.
   */
  public static LinearTransformationBuilder mapping(double x1, double y1) {
    checkArgument(isFinite(x1) && isFinite(y1));