(* Title: Sequents/LK/Nat.thy
Author : Lawrence C Paulson , Cambridge University Computer Laboratory
Copyright 1999 University of Cambridge
*)
section ‹
Nat
"../LK"
nat
nat :: "term" ..
Zero :: nat (‹ 0› ) and
Suc :: "nat ==> nat" and
rec :: "[nat, 'a, [nat,'a] ==> 'a] ==> 'a"
induct: "[ $H ⊨ $E, P(0), $F;
∧ x. $H, P(x) ⊨ $E, P(Suc(x)), $F] ==> $H ⊨ $E, P(n), $F" and
Suc_inject: "⊨ Suc(m) = Suc(n) ⟶ m = n" and
Suc_neq_0: "⊨ Suc(m) ≠ 0" and
rec_0: "⊨ rec(0,a,f) = a" and
rec_Suc: "⊨ rec(Suc(m), a, f) = f(m, rec(m,a,f))"
add :: "[nat, nat] ==> nat" (infixl ‹ +› 60)
where "m + n == rec(m, n, λx y. Suc(y))"
Suc_neq_0 [simp]
Suc_inject_rule: "$H, $G, m = n ⊨ $E ==> $H, Suc(m) = Suc(n), $G ⊨ $E"
by (rule L_of_imp [OF Suc_inject])
Suc_n_not_n: "⊨ Suc(k) ≠ k"
apply (rule_tac n = k in induct)
apply simp
apply (fast add!: Suc_inject_rule)
done
add_0: "⊨ 0 + n = n"
apply (unfold add_def)
apply (rule rec_0)
done
add_Suc: "⊨ Suc(m) + n = Suc(m + n)"
apply (unfold add_def)
apply (rule rec_Suc)
done
add_0 [simp] add_Suc [simp]
add_assoc: "⊨ (k + m) + n = k + (m + n)"
apply (rule_tac n = "k" in induct)
apply simp_all
done
add_0_right: "⊨ m + 0 = m"
apply (rule_tac n = "m" in induct)
apply simp_all
done
add_Suc_right: "⊨ m + Suc(n) = Suc(m + n)"
apply (rule_tac n = "m" in induct)
apply simp_all
done
"(∧ n. ⊨ f(Suc(n)) = Suc(f(n))) ==> ⊨ f(i + j) = i + f(j)"
apply (rule_tac n = "i" in induct)
apply simp_all
done
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(vorverarbeitet am 2026-06-10)
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