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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 _merge_summary(in_files, out_file, data):
 """Create one big summary file for disambiguation from multiple splits. """

    if not utils.file_exists(out_file):
        with file_transaction(data, out_file) as tx_out_file:
            with open(tx_out_file, "w") as out_handle:
                for i, in_file in enumerate(in_files):
                    with open(in_file) as in_handle:
                        for j, line in enumerate(in_handle):
                            if j == 0:
                                if i == 0:
                                    out_handle.write(line)
                            else:
                                out_handle.write(line)
    return out_file