Solving methods > Before starting :

A sudoku puzzle comprises 9 rows, 9 columns and 9 block. Each of them must contain all numbers from 1 to 9. The following concepts are there to help you understanding the methods to solve a sudoku.

• The cell is the base unit of sudoku wich must be assigned a number from 1 to 9.
  Each cell is part of three groups at a time: one row, one column and one block.
  
• The groups
  
  • The row has nine cells disposed horizontally
    
  • The column has nine cells disposed vertically
    
  • The block has nine cells disposed in 3x3 squares, the puzzle comprises nine of these blocks.
    
• The segment is a row of three cells within a block, arranged either horizontally or vertically.
  Each block thus containing 6 segments, and each row/column containing 3.
  A segment is therefore part of both a block and a row or a block and a column.
  
• The candidates are the possible numbers for a given cell. They are shown in small charactères.
  When only one candidate remains for a cell, then this number can be assigned to that cell.
  When there are two candidates for a cell, one speaks of a pair, triplet for three and quad for four candidates.
  

Each method is illustrated by a graphic.
Number's size and color help you to understand these examples :

• In big , the numbers allready assigned to a cell
• In small, the candidates (possible numbers for a cell)
• In blue, the cells wich permit to make a deduction
• In yellow, the cells where the deduction applies

The methods for resolving a sudoku are classified from the simplest to the most complex.
In general, one should allways exhaust one method before using the next more complex one.
One can then try again with the simpler method , and so forth.

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