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Exercise 2.6
A variant of string-of-char-list? **

The function string-of-char-list? was programmed with use of a help function which we called string-of-char-list-1? on this slide. The help function was programmed side by side with string-of-char-list?. As an altertive, string-of-char-list-1? could be programmed as a local function of string-of-char-list? Please do that, using an appropriate name binding form.

The help function keeps track of an index i in an additional parameter. It is possible to program string-of-char-list? without use of a help function. This function should iterate over shorter and shorter text strings. Please do that now. Consider the efficiency of this function and our original version of string-of-char-list?. (The function substring is useful).