------
## 最终结论
```python
def canPrint(targetGrid):
    m, n = len(targetGrid), len(targetGrid[0])
    
    # Check if each color forms a solid rectangle
    color_rectangles = {}
    
    for i in range(m):
        for j in range(n):
            color = targetGrid[i][j]
            if color not in color_rectangles:
                color_rectangles[color] = [i, i, j, j]  # top, bottom, left, right
            
            # Update the boundaries of the rectangle for this color
            color_rectangles[color][0] = min(color_rectangles[color][0], i)  # top
            color_rectangles[color][1] = max(color_rectangles[color][1], i)  # bottom
            color_rectangles[color][2] = min(color_rectangles[color][2], j)  # left
            color_rectangles[color][3] = max(color_rectangles[color][3], j)  # right
    
    used_colors = set()
    
    # Check if each rectangle is consistent with the targetGrid
    for color, (top, bottom, left, right) in color_rectangles.items():
        if color in used_colors:
            return False  # Color already used
        
        used_colors.add(color)
        
        # Verify that the rectangle is filled with the same color
        for i in range(top, bottom + 1):
            for j in range(left, right + 1):
                if targetGrid[i][j] != color:
                    return False
    
    return True

# Example Usage:
print(canPrint([[1,1,1,1],[1,2,2,1],[1,2,2,1],[1,1,1,1]]))  # Output: true
print(canPrint([[1,1,1,1],[1,1,3,3],[1,1,3,4],[5,5,1,4]]))  # Output: true
print(canPrint([[1,2,1],[2,1,2],[1,2,1]]))                  # Output: false
print(canPrint([[1,1,1],[3,1,3]]))                          # Output: false
```