anchor.diff:      }
     }
   
  -  _Symbol _getEnteringSymbolForObjectiveRow(_Row objective) {
  +  _Symbol _enteringSymbolForObjectiveRow(_Row objective) {
       Map<_Symbol, double> cells = objective.cells;
   
       for (_Symbol symbol in cells.keys) {
  
positive.code:     return Result.success;
    }
  
    _Symbol _getDualEnteringSymbolForRow(_Row row) {
      _Symbol entering;
  
      double ratio = double.MAX_FINITE;
  
negative.code: 
    Solver operator <<(Constraint c) => this..addConstraint(c);
  
    _Symbol _symbolForVariable(Variable variable) {
      _Symbol symbol = _vars[variable];
  
      if (symbol != null) {
  