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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 plus_nat (Suc m) n = plus_nat m (Suc n)
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| plus_nat Zero_nat n = n;
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fun times_nat (Suc m) n = plus_nat n (times_nat m n)
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| times_nat Zero_nat n = Zero_nat;
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end; (*struct Nat*)
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structure Codegen =
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struct
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fun fac (Nat.Suc n) = Nat.times_nat (Nat.Suc n) (fac n)
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| fac Nat.Zero_nat = Nat.Suc Nat.Zero_nat;
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end; (*struct Codegen*)
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