### Table 5: The Take Out Method The unfold tactic rewrites recursively de ned functions using their step equations. Unfolding is illustrated in gures 1 and 3. The speci cation of the unfold tactic is given in table 6. The preconditions slot speci es that the input must be an expression containing a primitive recursive function whose recursive argument has s as its dominant function. The e ects slot asserts that the output will be an expression obtained by rewriting the input expression using the step equation of the recursive function. The tactic slot gives the de nition of a program, unfold, which takes a position and a formula and returns that formula with the term at that position rewritten using the step equation. Name unfold([NjPosn]) Declarations 8Exp1 2 exprs; 8Exp2 2 exprs; 8N 2 nums; 8Posn 2 posns: Input

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