i. Sun~nary of String Theory In writing a grammar of a natural language, one is faced with the problem of expressing grammatica For example, in the sentence form N V N (N, noun: V, verb), the subject N and the verb V must agree in number: The boy eats the meat; ~ The boys eats the meat. Or, in the sequence Q N 1 P N 2 (Q a number; P, preposition), e.g., five feet in length, N 1 and N 2 are of particular subclasses: ~ five feet in •beauty. One of the theories of linguistic structure which is

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... icularly relevant to this problem is linguistic string analysis•[1]. In this theory, the major syntactic structures of English are stated as a set of elementary strings (a string is a sequence of word categories, e.g., N V____NN, N V P N, eta). Each sentence of the language consists of one elementary sentence (its center string) plus zero or more elementary adjunct strings which are adjoined either to the right or left or in place of particular elements of other elementary strings in the sentence. 17.~ The elementary strings can be grouped into classes according to how and where they can be inserted into other strings. If Y = X 1 X 2 . . . X n is an elementary string, X ranging over the category symbols, the following classes of strings are defined: -1-~X left adjuncts of X: adjoined to a string Y to the left of X in Y, or to the left of an ~X adjoined to Y in this manner. r X right adjuncts of X: adjoined to a string Y to the right of X in Y, or to the right of an r X adjoined to Y in this manner. nX replacement strings of X: adjoined to a string Y, replacing X in Y. Sy sentences adjuncts of the string Y, adjoined to the left of X 1 or after X i in Y (l~ i ~ n), or to the right of an Sy adjoined to Y in this manner. in Y (i< i < n), or to Cy, i conjunctional strings of Y, conjoined after X i _ _ the right of a Cy, i adjoined to Y in this manner. z center strings, not adjoined to any string. These string-class definitions, with various restrictions on the repetition ~and order of members of the classes, constitute rules of combination on the elementary strings to form sentences. Roughly speaking, a center string is the skeleton of a sentence and the adjuncts are modifiers. An example of a left adjunct of N is the adjective green in the green blackboard. A right adjunet of N is the clause whom we met in the man whom we met. A replacement formula of N is, for example, what he said in the sentence What he said was interesting. The same sentence with a noun instead of a noun replacement string might be The lecture was interesting. Examples of sentence adjuncts are in general, at this time, since he left. The c strings have coordinating conjunctions at their head. An example is but left in He was here but left. Examples of center strings are He understood and also We wondered whether he understood. The grammatical dependencies are expressed by restrictions on the strings as to the word subcategories which can occur together in a string or in strings related by the rules of combination. Thus, in the center string N 1 V N2, the