1. A method for indexing a plurality of electronic handwritten documents, each of which includes a plurality of output symbols ordered in an output sequence, each document being modeled by a respective Hidden Markov Model (HMM), the Hidden Markov Models having a common alphabet including n symbols, and a common output sequence length of T symbols, where n and T are integers, the method comprising the steps of: (a) establishing an index of symbols, each symbol being a feature vector, the index having T levels, each level between zero and T-1 having a respective minimum probability value, each level having at least one node; (b) indexing the symbols in one of the documents without translating the symbols into one of a known character and a known pictograph by performing, for each node in one of the levels of the index, the steps of: (1) determining a probability that a symbol stored in said node represents a corresponding output symbol in the one document, using the respective HMM for the one document, (2) adding a node in a next level of the index, if the probability determined in step (b)(1) exceeds the minimum probability value of the one level and the next level is between the one.sup.th level and the T-1.sup.th level, (3) executing step (b) for the added node in the next level, if the node is added in step (b)(2), and (4) adding a pointer to the one document in a list of pointers stored in a node in the T.sup.th level of the index, if the next level is the T.sup.th level and the probability determined in step (b)(1) is greater than the minimum probability value of the T-1.sup.th level; and (c) repeating step (b), for each of the plurality of documents other than the one document.