Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A stretcher bar is used to construct a wooden stretcher frame used by artists to mount their canvases. They are traditionally a wooden framework support on which an artist fastens a piece of canvas. They are also used for small-scale embroidery to provide steady tension, affixing the edges of the fabric with push-pins or a staple gun before beginning to sew, and then removing it from the stretcher when the work is complete. Stretchers are usually in the shape of a rectangle, although shaped canvases are also possible. Since a stretcher is simply a frame, it can be constructed in a variety of ways. The differences in construction have to do with how the corners are built. Commercially available pre-fabricated stretchers come in segments with interlocking corners, that can be fit together like puzzle pieces. Corner supports can also be made using simple woodworking techniques, however.
In writing Mystery of Sudoku I had an idea about creating an exceptionally hard puzzle. The result of this endeavor is a wide range of DDT puzzles, some of which will be included in this collection. DDT puzzles are another variant of Classic Sudoku puzzles, All FIELDS contain GIVEN NUMBERS whereby up to nine numbers can be given in a single FIELD.Despite similarities, familiarity with Classic Sudoku Rules is not necessary as during the solving process, all CORRECT NUMBERS are obtained, using only DDT RECTANGLE (¿). There are easier and harder puzzles to suit everybody's taste and preference.