def is_valid_combination( row ):
    """
    Should return True if combination is valid and False otherwise.
    
    Test row that is passed here can be incomplete.
    To prevent search for unnecessary items filtering function
    is executed with found subset of data to validate it.
    """

    n = len(row)
    if n>1:
        # Brand Y does not support Windows 98
        if "98" == row[1] and "Brand Y" == row[0]:
            return False
        # Brand X does not work with XP
        if "XP" == row[1] and "Brand X" == row[0]:
            return False
    if n > 4: 
        # Contractors are billed in 30 min increments
        if "Contr." == row[3] and row[4] < 30:
            return False
    
    return True