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Pointers and recursive type definitions complicate the algorithm for determining structural equivalence of types. Consider, for example, the following definitions: type A= record x : pointer to B y : real type B= record x : pointer to A y : real The simple definition of structural equivalence given in Section 7.2.1 (expand the subparts recursively until all you have is a string of built-in types and type constructors; then compare them) does not work: we get an infinite expansion (type A= record x : pointer to record x : pointer to record x : pointer to record...). The obvious reinterpretation is to say two types A and B are equivalent if any sequence of field selections, array subscripts, pointer dereferences, and other operations that takes one down into the structure of A, and that ends at a built-in type, always ends at the same built-in type when used to dive into the structure of B (and encounters the same field names along the way). Under this reinterpretation, A and B above have the same type. Give an algorithm based on this reinterpretation that could be used in a compiler to determine structural equivalence. (Hint: the fastest approach is due to J. Kr'al [Kr'a73]. It is based on the algorithm used to find the smallest deterministic finite automaton that accepts a given regular language. This algorithm was outlined in