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Exercise 2.73

a.

There are no operators for constant or variable expressions so the operator expression can’t works and give a correct type with this representation (number and variables are not tagged). # b. Here is my code, it’s the basic derivation code, it only works with two operands and it doesn’t simplify expressions.

c.

d.

We only need to reverse the index of each procedure:

Note that you can separate the procedures in different packages if you want (not really needed in this exercise).