try this (C# syntax for the example)

Rectangle rect = new Rectangle( 1,1,3,3); // make a rectangle at 1,1 that is
3 wide and 3 high.

Debug.Assert (rect.Left == 1); // true
Debug.Assert (rect.Top == 1); // true

// right and bottom should be 3,3

Debug.Assert (rect.Right == 3); // FALSE
Debug.Assert (rect.Bottom == 3); // FALSE ?? huh

Debug.Assert (rect.Right == 4); // true - what gives?
Debug.Assert (rect.Bottom == 4); // true

Debug.Assert(rect.Contains(1,1)); // true
Debug.Assert(rect.Contains(3,3)); // true
Debug.Assert(rect.Contains(4,4)); // FALSE - hmmm

BUT if we adjust the contructor to give us the right and bottom we expect,
the rectangle will no longer Contain the correct pixels!

Rectangle rect = new Rectangle( 1,1,3-1,3-1); // make a rectangle at 1,1
that is 3 wide and 3 high.

Debug.Assert (rect.Right == 3); // true
Debug.Assert (rect.Bottom == 3); // true

BUT -

Debug.Assert(rect.Contains(3,3)); // FALSE