begin
  var source := string.Empty;
  var a0 := source[:];
  var a1 := source[:1];
  var a2 := source[1:];
  var a3 := source[1:1];
  
  var b0 := source[::1];
  var b1 := source[1::1];
  var b2 := source[1:1:1];
end.