<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def set_vars(env):
 """Set MWCW_VERSION, MWCW_VERSIONS, and some codewarrior environment vars MWCW_VERSIONS is set to a list of objects representing installed versions MWCW_VERSION is set to the version object that will be used for building. MWCW_VERSION can be set to a string during Environment construction to influence which version is chosen, otherwise the latest one from MWCW_VERSIONS is used. Returns true if at least one version is found, false otherwise """

    desired = env.get('MWCW_VERSION', '')

    # return right away if the variables are already set
    if isinstance(desired, MWVersion):
        return 1
    elif desired is None:
        return 0

    versions = find_versions()
    version = None

    if desired:
        for v in versions:
            if str(v) == desired:
                version = v
    elif versions:
        version = versions[-1]

    env['MWCW_VERSIONS'] = versions
    env['MWCW_VERSION'] = version

    if version is None:
      return 0

    env.PrependENVPath('PATH', version.clpath)
    env.PrependENVPath('PATH', version.dllpath)
    ENV = env['ENV']
    ENV['CWFolder'] = version.path
    ENV['LM_LICENSE_FILE'] = version.license
    plus = lambda x: '+%s' % x
    ENV['MWCIncludes'] = os.pathsep.join(map(plus, version.includes))
    ENV['MWLibraries'] = os.pathsep.join(map(plus, version.libs))
    return 1