### Orientation

Most of the applications I build have client designs
& data so I must be extremely protective of their materials in all forms.
The following game application demonstrates some user interface & logic that
is not proprietary.

### Introduction

This set of pages is not an introduction to
Sudoku. I will assume that the reader is already knowledgeable, even a
sophisticated player. Much of what is presented will not make any sense unless
the reader has attempted to understand and solve the hardest logic bound
puzzles, the extremely difficult puzzles.

Extreme difficulty will be defined here as puzzles requiring the
following array of solution strategies. (examples will be supplied on
the following pages)

- Sub-row/column elimination
- 2-cell chains (row/column or block (RCB))
- Exclusive pairs RCB
- 3-cell chains RCB
- X-wing
- Swordfish
- 4-cell chains RCB

Extreme difficulty further means that after the application of a
strategy in the hierarchy above, many of the previous strategies must be
re-applied. Thus several layers of the more complex strategies (i. e.
swordfish) must be solved sequentially to arrive at a solution.

Logic bound grids are defined as having a single solution.

The application presented is not a puzzle solver, it is a
helper. There are plenty of
online
puzzle solvers. By helper I mean the application implements
my particular solution process.

In addition, the application allows the user to re-engineer
puzzles for different looks. This permits the re-use of an
extremely difficult grid in many different forms. This becomes
important once a survey of online puzzles has been completed. I only
found 18 unique extremely difficult grids online. Not only can one
re-engineer puzzles, more aesthetically pleasing, symmetric puzzles
can be assembled (see examples).