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structure ROOT =
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struct
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structure Nat =
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struct
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datatype nat = Zero_nat | Suc of nat;
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fun less_nat Zero_nat (Suc n) = true
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| less_nat n Zero_nat = false
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| less_nat (Suc m) (Suc n) = less_nat m n;
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fun minus_nat (Suc m) (Suc n) = minus_nat m n
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| minus_nat Zero_nat n = Zero_nat
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| minus_nat y Zero_nat = y;
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end; (*struct Nat*)
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structure Codegen =
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struct
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fun pick ((k, v) :: xs) n =
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(if Nat.less_nat n k then v else pick xs (Nat.minus_nat n k));
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end; (*struct Codegen*)
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end; (*struct ROOT*)
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