Lesson 4

It helps to put numbers in the top of the squares when you have narrowed it down to 2 squares.
I do not recommend putting the numbers in the squares that could go there. 
Fill in as many numbers and put notation numbers at the top of squares from numbers 1 through 9.
Go through them a second time.

Then look at the rows and columns.  Find the ones that have 1, 2, 3, and then even 4 missing numbers.
If there is only one number missing, then obviously fill it in. 
If there are 2, 3, or 4 missing, then put the numbers that are missing at the end of the row or column.

Look at the bottom row.  The 1, 2, 3, in the BR box have those three squares locked up.  The other three empty squares in that row are missing 4, 5, and 6.  The 4 goes into the red square at the bottom left because 5 is already in that box and the 6 is above
it in that column. 

In the row third from the bottom, the 1, 3, 6, and 9 are missing.  In the red empty square, look above and below in that column. 
There is a 1, 6, and 9 in that column.  So therefore the 3 goes into that square.  Then you will know where the 3,6,8 go in the
TM box. 

NEXT LESSON 5