.. py:function:: create_prj_dyn(flow, path, default)

   
   Return the expression tree for the dynamic projection operator.


   :Parameters:

       **flow** : :obj:`EX`
           Input flow of the projection.

       **path** : :obj:`Union`\[:obj:`EX`, :obj:`List`\[:obj:`EX`]]
           Elements of the path, which is a label, index, or variable.

       **default** : :obj:`EX`
           Default value for the projection when the path is incorrect.

   :Returns:

       :obj:`ET`
           ..













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