You are given three grids, where each of them is 5 by 5 in size.
Grids have empty cells marked with "▢" and filled cells marked with "X".
Your task is to generate a referring expression that best describes the target grid while distinguishing it from the two other distractor grids.
The first grid is the target grid, and the following two grids are the distractors.

Target grid:

▢ ▢ ▢ ▢ X
X ▢ X ▢ ▢
▢ ▢ X ▢ X
X ▢ X ▢ ▢
X X ▢ ▢ X

Distractor grid 1:

X X ▢ ▢ X
X ▢ X ▢ ▢
X ▢ ▢ X ▢
▢ ▢ X ▢ ▢
▢ X ▢ X ▢

Distractor grid 2:

▢ ▢ ▢ ▢ ▢
▢ ▢ ▢ ▢ ▢
▢ X ▢ X ▢
X X X ▢ X
X X X ▢ X

Instruction: Describe the target grid.
Generate the referring expression starting with the tag "Expression: " for the given target grid. Omit any other text.
Expression: The grid has a single "X" in the top row, followed by a checkerboard pattern of "X"s in the remaining cells, except for the bottom row which has "X"s in the first and last positions.<|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|><|im_end|>
assistant
Expression: Top left 3x3 region
assistant