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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 is_unix_like(platform=None):
 """Returns whether the given platform is a Unix-like platform with the usual Unix filesystem. When the parameter is omitted, it defaults to ``sys.platform`` """

    platform = platform or sys.platform
    platform = platform.lower()
    return platform.startswith("linux") or platform.startswith("darwin") or \
            platform.startswith("cygwin")