anchor.diff:   * Returns the angle between the positive x-axis and the vector ([b],[a]).
    * The result, in radians, is in the range -PI..PI.
    *
  - * If [b] is positive, this is the same as [:atan(b/a):].
  + * If [b] is positive, this is the same as `atan(b/a)`.
    *
    * The result is negative when [a] is negative (including when [a] is the
    * double -0.0).
  
positive.code: /**
   * Converts [x] to a double and returns the arc cosine of the value.
   *
   * Returns a value in the range -PI..PI, or NaN if [x] is outside
   * the range -1..1.
   */
  external double acos(num x);
  
  /**
   * Converts [x] to a double and returns the arc sine of the value.
   * 
   * Returns a value in the range -PI..PI, or  NaN if [x] is outside
   * the range -1..1.
   */
  external double asin(num x);
  
  /**
   * Converts [x] to a dobule and returns the arc tangent of the value.
   * 
   * Returns a value in the range -PI/2..PI/2, or NaN if [x] is NaN.
   */
  external double atan(num x);
  
negative.code: /**
   * Converts [x] to a double and returns the natural exponent, [E],
   * to the power [x].
   *
   * Returns NaN if [x] is NaN.
   */
  external double exp(num x);
  
  /**
   * Converts [x] to a double and returns the natural logarithm of the value.
   *
   * Returns negative infinity if [x] is equal to zero.
   * Returns NaN if [x] is NaN or less than zero.
   */
  