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definitions of complex data manipulations, such as string concatenation, whereas this report has dealt exclusively with environment and control operations. (Also, as a matter of taste, we find SCHEME a simpler and more tractable language to deal with than the low-level dialect of PL/I used in [Carter], partly because of its closeness to lambda-calculus and partly because SCHEME inherits from LISP the natural ability to deal with representations of its own programs.)