anchor.diff:  
   part of dart.core;
   
  -/// An arbitrarily large integer.
  +/// An arbitrarily large integer value.
  +///
  +/// Big integers are signed and can have an arbitrary number of
  +/// significant digits, only limited by memory.
   abstract class BigInt implements Comparable<BigInt> {
  +  /// A big integer with the numerical value 0.
     external static BigInt get zero;
  +
  +  /// A big integer with the numerical value 1.
     external static BigInt get one;
  +
  +  /// A big integer with the numerical value 2.
     external static BigInt get two;
   
     /// Parses [source] as a, possibly signed, integer literal and returns its
  
positive.code:   /// for zero, which is its own negation.
    BigInt operator -();
  
    /// Addition operator.
    BigInt operator +(BigInt other);
  
    /// Subtraction operator.
    BigInt operator -(BigInt other);
  
    /// Multiplication operator.
    BigInt operator *(BigInt other);
  
    /// Division operator.
    double operator /(BigInt other);
  
    /// Truncating division operator.
    ///
    /// Performs a truncating integer division, where the remainder is discarded.
    ///
  
negative.code:   /// This maps any integer `x` to `-x - 1`.
    BigInt operator ~();
  
    /// Whether this big integer is numerically smaller than [other].
    bool operator <(BigInt other);
  
    /// Whether [other] is numerically greater than this big integer.
    bool operator <=(BigInt other);
  
    /// Whether this big integer is numerically greater than [other].
    bool operator >(BigInt other);
  
    /// Whether [other] is numerically smaller than this big integer.
    bool operator >=(BigInt other);
  
    /// Compares this to `other`.
  