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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 makeDoubleLinked(dom, parent=None):
 """ Standard output from `dhtmlparser` is single-linked tree. This will make it double-linked. Args: dom (obj):
 :class:`.HTMLElement` instance. parent (obj, default None):
 Don't use this, it is used in recursive call. """

    dom.parent = parent

    for child in dom.childs:
        child.parent = dom
        makeDoubleLinked(child, dom)