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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 DocbookXslt(env, target, source=None, *args, **kw):
 """ A pseudo-Builder, applying a simple XSL transformation to the input file. """

    # Init list of targets/sources
    target, source = __extend_targets_sources(target, source)
    
    # Init XSL stylesheet
    kw['DOCBOOK_XSL'] = kw.get('xsl', 'transform.xsl')

    # Setup builder
    __builder = __select_builder(__lxml_builder, __libxml2_builder, __xsltproc_builder)
    
    # Create targets
    result = []
    for t,s in zip(target,source):
        r = __builder.__call__(env, t, s, **kw)
        env.Depends(r, kw['DOCBOOK_XSL'])
        result.extend(r)

    return result