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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def contracts_source_path_with_stem(stem):
 """The directory remapping given to the Solidity compiler."""

    return {
        'lib': _BASE.joinpath(stem, 'lib'),
        'raiden': _BASE.joinpath(stem, 'raiden'),
        'test': _BASE.joinpath(stem, 'test'),
        'services': _BASE.joinpath(stem, 'services'),
    }