begin
  //var s := '012345';
  var a:= Arr(0,1,2,3,4,5);
  var a1 := a?[-1:];
  Assert(a1.SequenceEqual(Seq(0,1,2,3,4,5)));
  a1 := a?[1:6];
  Assert(a1.SequenceEqual(Seq(1,2,3,4,5)));
  a1 := a?[-2::2];
  Assert(a1.SequenceEqual(Seq(0,2,4)));
  a1 := a?[3:-2:-1];
  Assert(a1.SequenceEqual(Seq(3,2,1,0)));
  a1 := a?[4:-2:-2];
  Assert(a1.SequenceEqual(Seq(4,2,0)));
  var l:= Lst(0,1,2,3,4,5);
  var l1 := l?[-1:];
  Assert(l1.SequenceEqual(Seq(0,1,2,3,4,5)));
  l1 := l?[1:6];
  Assert(l1.SequenceEqual(Seq(1,2,3,4,5)));
  l1 := l?[-2::2];
  Assert(l1.SequenceEqual(Seq(0,2,4)));
  l1 := l?[3:-2:-1];
  Assert(l1.SequenceEqual(Seq(3,2,1,0)));
  l1 := l?[4:-2:-2];
  Assert(l1.SequenceEqual(Seq(4,2,0)));
  var s := '012345';
  var s1 := s?[-1:];
  Assert(s1.Equals('012345'));
  s1 := s?[2:7];
  Assert(s1.Equals('12345'));
  s1 := s?[-1::2];
  Assert(s1.Equals('024'));
  s1 := s?[4:-2:-1];
  Assert(s1.Equals('3210'));
  s1 := s?[5:-2:-2];
  Assert(s1.Equals('420'));
end.