anchor.diff:  
   /**
    * Natural logarithm of 10.
  + *
  + * The natural logarithm of 10 is the number such that `pow(E, LN10) == 10`.
  + * This value is not exact, but it is the closest representable double to the
  + * exact mathematical value.
    */
   const double LN10 = 2.302585092994046;
   
   /**
    * Natural logarithm of 2.
  + *
  + * The natural logarithm of 2 is the number such that `pow(E, LN2) == 2`.
  + * This value is not exact, but it is the closest representable double to the
  + * exact mathematical value.
    */
   const double LN2 = 0.6931471805599453;
   
  
positive.code: 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/2..PI/2, or NaN if [x] is outside
   * the range -1..1.
  
negative.code: /**
   * A variant of [atan].
   *
   * Converts both arguments to [double]s.
   *
   * Returns the angle in radians between the positive x-axis
   * and the vector ([b],[a]).
   * The result is in the range -PI..PI.
   *
   * If [b] is positive, this is the same as `atan(b/a)`.
   *
  