theory ConstOn
imports Main
begin
definition const_on :: "('a → 'b) → 'a set → 'b → bool"
where "const_on f S x = (∀ y ∈ S . f y = x)"
lemma const_onI[intro]: "(∧y. y ∈ S ==> f y = x) ==> const_on f S x"
by (simp add: const_on_def)
lemma const_onD[dest]: "const_on f S x ==> y ∈ S ==> f y = x"
by (simp add: const_on_def)
(*
lemma const_onE[elim]: "const_on f S r ==> x : S ==> r = r' ==> f x = r'"
*)
lemma const_on_insert[simp]: "const_on f (insert x S) y ⟷ const_on f S y ∧ f x = y"
by auto
lemma const_on_union[simp]: "const_on f (S ∪ S') y ⟷ const_on f S y ∧ const_on f S' y"
by auto
lemma const_on_subset[elim]: "const_on f S y ==> S' ⊆ S ==> const_on f S' y"
by auto
end
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*© Formatika GbR, Deutschland