def region_domains(board):
    """
    make list of tuples for each region to construct domains
    return dictionary of region : set of coord pairs
    """
    regionCoords={}    
    rowIndex=0
    for row in board:
        colIndex=0
        for colVal in row:
            if colVal in regionCoords:
                regionCoords[colVal].add((rowIndex,colIndex))
            else:
                regionCoords[colVal]=set()
                regionCoords[colVal].add((rowIndex,colIndex))
            colIndex +=1
        rowIndex +=1
    return regionCoords