(i) Although perhaps too inefficient to be a final solution, LISP is still a very useful language with which to illustrate the features of a new concept of algorithm representation. It is especially easy to use LISP to design an interpreter for a language similar to, but different in significant ways from, LISP itself. (ii) The program described in this paper is quite limited with regard to its implementation of both LISP and the incremental computer. If a more complete experimental system were desired, the present system could easily be extended in any of several directions. For example, in LISP, allowance could be made for the use of functions defined by machine-language subroutines, and the use of special forms. In the incremental computer, threshold conditions could be inserted to allow partial evaluation and simplification of conditional expressions. (iii) Replacing .alJ bound variables by new symbols is too brutal a solution to the "conflict" problem; the resulting expressions become quite unreadable. Bound variables frequently have mnemonic significance, and therefore should not be changed unless absolutely necessary. A more sophisticated program would identify those symbols which actually caused a conflict, and then perhaps replace each offending symbol with one whose spelling is different but similar. (iv) When a function of an indefinite argument is evaluated, the form in the argument is substituted for each occurrence of a variable in the form in the function definition. Similarly, when a function has omitted arguments, those arguments which were net omitted are each evaluated and substituted for each occurrence of variables in the form in the function definition. In the interest of saving computer space, we must be sure that what is substituted is a reference to an expression, not a copy of the expression. In the interest of readability, perhaps the print-outs should similarly contain references to repeated subexpressions, e.g., in the form of A-expressions, rather than fully-expanded expressions. Bibl iographl and B . Raphael: Man-computer information systems, l e c t u r e notes of a two week course UCLA Physical Sciences Extension, July 2030, 1964. L. A . Lombardi: Zwei B e i t r a g e zur Morphologie und Syntax d e k l a r a t i v e r Systernsprachen, Akten der 1962 Jahrestagung der Gesellschaft f ü r angewandte Mathematik Mechanik (GAMM), Bonn (1962); Z e i t s c h r . angew. Math. Mech. (42) Sonderhef t. T27-T29. : On t h e Control of t h e Data Flow by Means of Recursive Functions, Proc. Symp. "Symb o l i c Lanquages i n Data Processing", International Computation Center, Roma, Gordon and Breach, 1962, 173-186. : On Table Operatiny Alyorittims, Proc. 2nd IFIP Congress, Munchen (19621, s e c t i o n 14. : P r o s p e t t i v e per il c a l c o l o automatico, S c i e n t i a ( i n I t a l i a n and French) S e r i e s I V (57) 2 and 3 (1963). : Incremental data a s s i m i l a t i o n i n man-comput e r systems, Proc. 1 s t Congress of Associazione I t a l i a n a Calcolo Automatico (AICA), Bologna, May 20-22, 1963 ( i n p r e s s ) . D. G . Bobrow and B. Raphael: A Comparison of List-processing Cornputer Languages, Comm. ACM, expected p u b l iThe c a t Compatible i o n April Time-Sharing o r May, 1964. MIT Computation Center: System: A Programmer's Guide, MIT Press, Cambridge, Mass., 1963. A. Church: The C a l c u l i of Lambda-Conversion, Princeton University Press, Princeton, N.J., 1941. The computer-related science (synnoetics) a t a L . Fein: ~ n i v e r s i tof~ t h e year 1975, American Scient i s t (49) (19611, 149-168; Datamation (7) 9 (19611, 34-41. L. A . Lombardi Work reported herein was p a r t l y supported by P r o j e c t MAC, an MIT research program sponsored by t h e Advanced Research P r o j e c t s Agency, Department of Defense, under Office of Naval Research Contract Number Nonr-4102(01). Reproduction i n whole or in p a r t i s permitted f o r any purpose of t h e United S t a t e s Government. Assoc. P r o f . of I n d u s t r i a l Management, MIT. Research A s s i s t a n t , Mathematics Dept., MIT.