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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 build_point_source_geometry(point_source):
 """ Returns the poing source geometry as a Node :param point_source: Point source model as an instance of the :class: `openquake.hazardlib.source.point.PointSource` :returns: Instance of :class:`openquake.baselib.node.Node` """

    xy = point_source.location.x, point_source.location.y
    pos_node = Node("gml:pos", text=xy)
    point_node = Node("gml:Point", nodes=[pos_node])
    upper_depth_node = Node(
        "upperSeismoDepth", text=point_source.upper_seismogenic_depth)
    lower_depth_node = Node(
        "lowerSeismoDepth", text=point_source.lower_seismogenic_depth)
    return Node(
        "pointGeometry",
        nodes=[point_node, upper_depth_node, lower_depth_node])