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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 split_window(pymux, variables):
 """ Split horizontally or vertically. """

    executable = variables['<executable>']
    start_directory = variables['<start-directory>']

    # The tmux definition of horizontal is the opposite of prompt_toolkit.
    pymux.add_process(executable, vsplit=variables['-h'],
                      start_directory=start_directory)