anchor.diff:  import 'dart:async';
   import 'dart:io';
  +
  +import 'package:more/more.dart';
   
   /// Matches the filename of a problem.
   final RegExp pattern = RegExp(r'\w+\d+\.dart$');
  
positive.code: }
  
  /// Iterator over all the Euler problems.
  Iterable<Problem> get problems => Directory.current.parent
      .listSync(recursive: true, followLinks: false)
      .whereType<File>()
      .where((file) => pattern.hasMatch(file.path))
      .map((file) => Problem(file));
  
  void main() {
    for (final problem in problems) {
  
negative.code:   String get path => file.path;
  
    /// Label of the problem.
    String get label => path.removePrefix('${Directory.current.path}/lib/');
  
    /// Tests if this is a valid filename.
    bool get isValid => pattern.hasMatch(label) && file.existsSync();
  
    /// Executes the problem synchronously.
    ProcessResult executeSync({List<String> arguments = const []}) =>
  