37. A search engine as claimed in claim 36 , wherein said index network obtains the product of said query vector and the text vector of the nodes of a level of said structure, and obtains said product for nodes of a succeeding level of said structure which are connected to nodes for which the product has exceeded a predetermined threshold.
38. A search engine as claimed in claim 37 , wherein the indices of nodes having a query vector node vector product higher than a predetermined threshold are output by said index network.