# Explanation why next cell has to be a certain value

I'm an absolute beginner and was stuck at the first puzzle of Sven's Sudoku Pad. I reached the following board state, where I noted for every cell which values were possible:

After a while I simply tried to brute force a solution. I set the value of the cell R7C4 to 5, which quickly resulted in a contradiction: I could not place a 7 in the bottom middle 3x3 block. After that I was able to solve the puzzle quite easily.

My question is which technique (instead of pure brute force) I should have applied here. I tried reading up on Y wings and similar techniques, but spotting and applying them are quite hard indeed.

• Out of curiosity, why do some cells have duplicate numbers? Mar 21 at 15:41
• @2012rcampion The little marks represent the Snyder notation which I initially conducted. For this I only jot down for values that have exactly 2 positions in a 3x3 grid. The center marks just note all the possible values that can go in a cell which helped me brute force it. Mar 21 at 16:21