This problem is related to the 17x17 challenge. See also Part 1 of this problem. Given a matrix in which each element is either 1, 2, 3, or 4, determine whether or not any rectangles are present. A rectangle is a formed whenever four instances of the same value appear in the corners of a rectangular region of the matrix.

Examples:

 Input  a = [ 4 1 2 4 1
              3 3 2 1 4
              3 2 4 1 1
              1 4 3 2 2
              1 1 1 4 4 ]
 Output tf is false

You can't form any rectangles here.

 Input a = [ 1 4 3 1
             3 1 4 1
             1 3 4 1
             1 1 2 3 ]
 Output tf is true

There is a rectangle: a([1 3],[1 4]) is [1 1; 1 1]