Any expression fonned with the operations of addition. multiplication. and negation represents explicitly a circuit containing only series and paraUel connections. Such a circuit will be called a series-parallel circuit. Each leller in an expression of this sort represents a make or break relay contact. or a switch blade and contact. To find the circuit requiring the least number of contacts. it is therefore necessary to manipulate the expression into the form in which the least number of letters appear. The theorems given above are always sufficient to do

Symbol x o X+Y Xy x' = Interpretation in Relay Circuits The circuit X The circuit is closed The circuit is open The series connection of circuits X and Y The parallel connection of circuits X and Y The circuit which is open when X is closed and closed when X is open The circuits open and close simultaneously Interpretation in the Calculus of Propositions The proposition X The proposition is false The proposition is true The proposition which is true if either X or Y is true The proposition which is true if both X and Y are true The contradictory of proposition X Each proposition implies the other

We are now in a position to demonstrate the equivalence of this calculus with certain elementary pans of the calculus of propositions. The algebra of logic 1-3, originated by George Boole, is a symbolic method of investigating logical relationships. The symbols of Boolean algebra admit of two logical interpretations. If interpreted in tenns of classes, the variables are not limited to the two possible values 0 and I. This interpretation is known as the algebra of classes. If, however, the tenns are taken to represent propositions, we have the calculus of propositions in which variables are limited to the values 0 and I,' as are the hindrance functions above.

We shall limit our treatment of circuits containing only relay contacts and switches. and therefore lit any given lime Ihe circuit between !lily two terminals must be either open (infinite impedance) or closed (zero impedance). Let us associate a symbol X.m or more simply X. with the tenninals a and b. This variable. a function of lime, will be called the hindrance of the two-terminal circuit a -b. The symbol 0 (zero) will be used In represent Ihe hindrance of a closed circuit. and lAe wmbol I (unity) In represent the hindrance of an open circuil.

The method of attack on these problcms may be described brieRy as follows: any circuit is represented by a set of equations, Ihe terms of the equations cOITesponding 10 the various relays and switches in the circuit. A calculus is developed for manipulating these equalions by simple mathematical most of which are similar 10 ordinary algebraic algorisms. This calculus is shown to be exactly analogolls tn the calculus of propositions used in Ihe symbolic study or logic. For the synthesis problem the desired characteristics arc first wrillcn Ii system of equations, lind the equations are then manipulated into the form represenling the simplest circuil. lllc: circuit may then be immcdilitcly lImwn rrom the equations. By this method it is always pm:-.iblc to find the simplest circuit containing only series and parallel cnnneclions, amI in some cases the simplest circuit containing any type of connection.

In the control and protective circuits of complex electrical systems it is frequently necessary 10 make intricluc interconnections of relay C0ll13CIS and switches. Examples of these circuits occur in automalic telephone exchanges, industril:ll molor-controi equipment. and in almost any circuits designed to perform complex operations automatically. In this paper Ii mathematical analysis of ccrtuin uf the propt!rties of such networks will be made. Particular anemion will be given to the prOblem of network synthesis. Given certain characteristics. it is required 10 find a circuit incorporating these characteristics. The solulion of this type of pmblcm is 1101 unique and methods of finding those particular circuits requiring the least number of relay contacts and switch blades will be studied. Methods will also be described for finding any number of circuit.s equivalent to tl given circuit in all operating characteristics.

In fact, shrinkingdimensions on an integrated structure makes it possible tooperate the structure at higher speed for the same powerper unit area.

In 1970, themanufacturing cost per component can be expected to beonly a tenth of the present cost.The complexity for minimum component costs has in-creased at a rate of roughly a factor of two per year(see graph). Certainly over the short term this rate can beexpected to continue, if not to increase. Over the longerterm, the rate of increase is a bit more uncertain, althoughthere is no reason to believe it will not remain nearlyconstant for at least ten years. That means by 1975, thenumber of components per integrated circuit for minimumcost will be 65 000.

This allows at least 500components per linear inch or a quarter million per squareinch.

Thus there is a minimum costat any given time in the evolution of the technology. Atpresent, it is reached when 50 components are used percircuit.

Silicon is likely to remain the basic material, althoughothers will be of use in specific applications. For example,gallium arsenide will be important in integrated microwavefunctions. But silicon will predominate at lower frequenciesbecause of the technology which has already evolvedaround it and its oxide, and because it is an abundant andrelatively inexpensive starting material.

The use of linear integrated circuitry is still restrictedprimarily to the military. Such integrated functions are ex-pensive and not available in the variety required to satisfy amajor fraction of linear electronics. But the first applicationsare beginning to appear in commercial electronics, partic-ularly in equipment which needs low-frequency amplifiersof small size.

Integrated circuits will lead to such wonders as homecomputers—or at least terminals connected to a centralcomputer—automatic controls for automobiles, and per-sonal portable communications equipment. The electronicwristwatch needs only a display to be feasible today.

65 000

It is useful to remember that the ELIZA program itself is merely a translating processor in the technical programming sense

A switch of objectives from the conceal­ment to the revelation of misunderstanding is seen as a precondition to making an ELIZA-like program the basis for an effective natural language man-machine com­munication system.

ELIZA in its use so far has had as one of its principal objectives the concealment of its lack of understanding.

A large part of whatever elegance may be credited to ELIZA lies in the fact that ELIZA maintains the illusion of understanding with so little machinery.

deserving of credibility. A certain danger lurks there.

ELIZA shows, if nothing else, how easy it is to create and maintain the illusion of understanding, hence perhaps of judgmen

Some subjects'have been very hard to convince that ELIZA (with its present script) is not human.

An important consequence of the editing facility built into ELIZA is that a given ELIZA script need not start out to be a large, full-blown scenario. On the contrary, it should begin as a quite modest set of keywords and transformation rules and permitted to be grown and molded as experience with it builds up.

Two problems now arise.

There is, however, another mechanism which causes the system to respond more spectacularly in the absence of a key. The word “MEMORY” is another reserved pseudo­keyword.

The system described so far is essentially one ■which selects a decomposition rule for the highest ranking key­word found in an input text, attempts to match that text according to that decomposition rule and, failing to make a match, selects the next reassembly rule associated with the matching decomposition rule and applies it to generate an output, text. It is, in other words, a system which, for the highest ranking keyword of a text, selects a specific decomposition and reassembly rule to be used in forming the output message.

The central issue is clcarty one of text manipulation, and at the heart of that issue is the concept of the trans­formation rule which has been said to be associated with certain keywords. The mechanisms subsumed under the slogan “transformation rule” are a number of Slipfunc­tions which serve to (1) decompose a data string according to certain criteria, hence to test the string as to whether it satisfies these criteria or not, and (2) to reassemble a decomposed string according to certain assembly specifica­tions.

Keywords and their associated transformation1 rules constitute the SCRIPT for a particular class of con­versation. An important property of ELIZA is that a script is data; i.e., it is not part of the program itself. Hence, ELIZA is not restricted to a particular set of recognition patterns or responses, indeed not even to any specific language. ELIZA scripts exist (at this writing) in Welsh and German as well as in English.

The gross procedure of the program is quite simple; the text is read and inspected for the presence of a. keyword.If such a word is found, the sentence is transformed according to a rule associated with the keyword, if not a content-free remark or, under certain conditions, an earlier transformation is retrieved. The text so computed or retrieved is then printed out.

It is said that to explain is to explain away. This maxim is nowhere so well fulfilled as in the area of computer programming, especially in what is called heuristic pro­gramming and artificial intelligence. For in those realms machines are made to behave in wondrous ways, often sufficient to dazzle even the most experienced observer. But once a particular program is unmasked, once its inner workings are explained in language sufficiently plain to induce understanding, its magic crumbles away; it stands revealed as a mere collection of procedures, each quite comprehensible. The observer says to himself “I could have written that”. With that thought he moves the program in question from the shelf marked "intelligent”, to that reserved for curios, fit to be discussed only with people less enlightened than he.

ELIZA is a program operating within the M A C time-sharingsystem at MIT which makes certain kinds of natural lan gu ageconversation between man and computer possible. Input sen­tences are analyzed on the basis of decomposition rules whichare triggered by key words appearin g in the input text.Responses are generated by reassembly rules associated withselected decomposition rules

An important consequence of the editing facility built into ELIZA is that a given ELIZA script need not start out to be a large, full-blown scenario. On the contrary, it should begin as a quite modest set of keywords and transformation rules and permitted to be grown and molded as experience with it builds

There is, however, another mechanism which causes the system to respond more spectacularly in the absence of a key. The word "MEMORY" is another reserved pseudo- keyw

Two problems now arise

The system described so far is ess(qltially one which selects ~t decomposition rule for the highest ranking key- word found in an input text, attempts to match that text according to that decomposition rule and, failing to make a match, selects the next reassembly rule associated with the matching decomposition rule and applies it. to generate an output texi. It is, in other words, a system which, for the highest ranking keyword of a text, selecta a speeifie decomposition and reassembly rule to be used ill forming the output message.

It is said that• to explain is to explain away. This maxim is nowhere so well fulfilled as in the area of computer programming, especially in what is ealled heuristic pro- gramming and artifieiM intelligence. For in those realms machines are made to behave in wondrous ways, often suftieient to dazzle even the most experim~eed observer. But once a particular program is unmasked, once its inner workings are explained in language sufficiently plain to induce understanding, its magic crumbles away; iL st~mds revealed as a mere collection of procedures, each quite comprehensible. The observer says to himself "I could have written that". With that thought he moves the program in question from the shelf m~trked "intelligent", to that reserved for curios, fit to be discussed only with people less enlightened than he.

ELIZA is a program operating within the MAC time-sharing system at MIT which makes certain kinds of natural language conversation between man and computer possible. Input sen- tences are analyzed on the basis of decomposition rules which are triggered by key words appearing in the input text. Responses are generated by reassembly rules associated with selected decomposition rules.