def checkNoCommonProblems(ds1, ds2, fname1, fname2):
    """
    Check that no common problems in two datasets
    Parameters:
    - ds1     -- 1-st dataset as dictionary of its problems
                 dictionary of problems of the dataset
                   key:    problem name
                   value:  Statistics of problem usage as DsProblemStat
    - ds2     -- 2-nd dataset as dictionary of its problems
                 similar to ds1
    - fname1  -- file name of 1-st dataset
    - fname2  -- file name of 2-nd dataset
    Returns number of errors found
    """
    _n_errors = 0
    _common_problems = frozenset(ds1.keys()).intersection(ds2.keys())
    if _common_problems:
        _n_errors = len(_common_problems)
        print(f"Error datasets {fname1} and {fname2} " +
              "have following {_n_errors} common problems:")
        print(_common_problems)
    return _n_errors