Theory Sprod

(*  Title:      HOL/HOLCF/Sprod.thy
    Author:     Franz Regensburger
    Author:     Brian Huffman
*)

section ‹The type of strict products›

theory Sprod
  imports Cfun
begin

default_sort pcpo


subsection ‹Definition of strict product type›

definition "sprod = {p::'a × 'b. p = ⊥ ∨ (fst p ≠ ⊥ ∧ snd p ≠ ⊥)}"

pcpodef ('a, 'b) sprod  ("(_ ⊗/ _)" [21,20] 20) = "sprod :: ('a × 'b) set"
  by (simp_all add: sprod_def)

instance sprod :: ("{chfin,pcpo}", "{chfin,pcpo}") chfin
  by (rule typedef_chfin [OF type_definition_sprod below_sprod_def])

type_notation (ASCII)
  sprod  (infixr "**" 20)


subsection ‹Definitions of constants›

definition sfst :: "('a ** 'b) → 'a"
  where "sfst = (Λ p. fst (Rep_sprod p))"

definition ssnd :: "('a ** 'b) → 'b"
  where "ssnd = (Λ p. snd (Rep_sprod p))"

definition spair :: "'a → 'b → ('a ** 'b)"
  where "spair = (Λ a b. Abs_sprod (seq⋅b⋅a, seq⋅a⋅b))"

definition ssplit :: "('a → 'b → 'c) → ('a ** 'b) → 'c"
  where "ssplit = (Λ f p. seq⋅p⋅(f⋅(sfst⋅p)⋅(ssnd⋅p)))"

syntax "_stuple" :: "[logic, args] ⇒ logic"  ("(1'(:_,/ _:'))")
translations
  "(:x, y, z:)" ⇌ "(:x, (:y, z:):)"
  "(:x, y:)" ⇌ "CONST spair⋅x⋅y"

translations
  "Λ(CONST spair⋅x⋅y). t" ⇌ "CONST ssplit⋅(Λ x y. t)"


subsection ‹Case analysis›

lemma spair_sprod: "(seq⋅b⋅a, seq⋅a⋅b) ∈ sprod"
  by (simp add: sprod_def seq_conv_if)

lemma Rep_sprod_spair: "Rep_sprod (:a, b:) = (seq⋅b⋅a, seq⋅a⋅b)"
  by (simp add: spair_def cont_Abs_sprod Abs_sprod_inverse spair_sprod)

lemmas Rep_sprod_simps =
  Rep_sprod_inject [symmetric] below_sprod_def
  prod_eq_iff below_prod_def
  Rep_sprod_strict Rep_sprod_spair

lemma sprodE [case_names bottom spair, cases type: sprod]:
  obtains "p = ⊥" | x y where "p = (:x, y:)" and "x ≠ ⊥" and "y ≠ ⊥"
  using Rep_sprod [of p] by (auto simp add: sprod_def Rep_sprod_simps)

lemma sprod_induct [case_names bottom spair, induct type: sprod]:
  "⟦P ⊥; ⋀x y. ⟦x ≠ ⊥; y ≠ ⊥⟧ ⟹ P (:x, y:)⟧ ⟹ P x"
  by (cases x) simp_all


subsection ‹Properties of \emph{spair}›

lemma spair_strict1 [simp]: "(:⊥, y:) = ⊥"
  by (simp add: Rep_sprod_simps)

lemma spair_strict2 [simp]: "(:x, ⊥:) = ⊥"
  by (simp add: Rep_sprod_simps)

lemma spair_bottom_iff [simp]: "(:x, y:) = ⊥ ⟷ x = ⊥ ∨ y = ⊥"
  by (simp add: Rep_sprod_simps seq_conv_if)

lemma spair_below_iff: "(:a, b:) ⊑ (:c, d:) ⟷ a = ⊥ ∨ b = ⊥ ∨ (a ⊑ c ∧ b ⊑ d)"
  by (simp add: Rep_sprod_simps seq_conv_if)

lemma spair_eq_iff: "(:a, b:) = (:c, d:) ⟷ a = c ∧ b = d ∨ (a = ⊥ ∨ b = ⊥) ∧ (c = ⊥ ∨ d = ⊥)"
  by (simp add: Rep_sprod_simps seq_conv_if)

lemma spair_strict: "x = ⊥ ∨ y = ⊥ ⟹ (:x, y:) = ⊥"
  by simp

lemma spair_strict_rev: "(:x, y:) ≠ ⊥ ⟹ x ≠ ⊥ ∧ y ≠ ⊥"
  by simp

lemma spair_defined: "⟦x ≠ ⊥; y ≠ ⊥⟧ ⟹ (:x, y:) ≠ ⊥"
  by simp

lemma spair_defined_rev: "(:x, y:) = ⊥ ⟹ x = ⊥ ∨ y = ⊥"
  by simp

lemma spair_below: "x ≠ ⊥ ⟹ y ≠ ⊥ ⟹ (:x, y:) ⊑ (:a, b:) ⟷ x ⊑ a ∧ y ⊑ b"
  by (simp add: spair_below_iff)

lemma spair_eq: "x ≠ ⊥ ⟹ y ≠ ⊥ ⟹ (:x, y:) = (:a, b:) ⟷ x = a ∧ y = b"
  by (simp add: spair_eq_iff)

lemma spair_inject: "x ≠ ⊥ ⟹ y ≠ ⊥ ⟹ (:x, y:) = (:a, b:) ⟹ x = a ∧ y = b"
  by (rule spair_eq [THEN iffD1])

lemma inst_sprod_pcpo2: "⊥ = (:⊥, ⊥:)"
  by simp

lemma sprodE2: "(⋀x y. p = (:x, y:) ⟹ Q) ⟹ Q"
  by (cases p) (simp only: inst_sprod_pcpo2, simp)


subsection ‹Properties of \emph{sfst} and \emph{ssnd}›

lemma sfst_strict [simp]: "sfst⋅⊥ = ⊥"
  by (simp add: sfst_def cont_Rep_sprod Rep_sprod_strict)

lemma ssnd_strict [simp]: "ssnd⋅⊥ = ⊥"
  by (simp add: ssnd_def cont_Rep_sprod Rep_sprod_strict)

lemma sfst_spair [simp]: "y ≠ ⊥ ⟹ sfst⋅(:x, y:) = x"
  by (simp add: sfst_def cont_Rep_sprod Rep_sprod_spair)

lemma ssnd_spair [simp]: "x ≠ ⊥ ⟹ ssnd⋅(:x, y:) = y"
  by (simp add: ssnd_def cont_Rep_sprod Rep_sprod_spair)

lemma sfst_bottom_iff [simp]: "sfst⋅p = ⊥ ⟷ p = ⊥"
  by (cases p) simp_all

lemma ssnd_bottom_iff [simp]: "ssnd⋅p = ⊥ ⟷ p = ⊥"
  by (cases p) simp_all

lemma sfst_defined: "p ≠ ⊥ ⟹ sfst⋅p ≠ ⊥"
  by simp

lemma ssnd_defined: "p ≠ ⊥ ⟹ ssnd⋅p ≠ ⊥"
  by simp

lemma spair_sfst_ssnd: "(:sfst⋅p, ssnd⋅p:) = p"
  by (cases p) simp_all

lemma below_sprod: "x ⊑ y ⟷ sfst⋅x ⊑ sfst⋅y ∧ ssnd⋅x ⊑ ssnd⋅y"
  by (simp add: Rep_sprod_simps sfst_def ssnd_def cont_Rep_sprod)

lemma eq_sprod: "x = y ⟷ sfst⋅x = sfst⋅y ∧ ssnd⋅x = ssnd⋅y"
  by (auto simp add: po_eq_conv below_sprod)

lemma sfst_below_iff: "sfst⋅x ⊑ y ⟷ x ⊑ (:y, ssnd⋅x:)"
  by (cases "x = ⊥", simp, cases "y = ⊥", simp, simp add: below_sprod)

lemma ssnd_below_iff: "ssnd⋅x ⊑ y ⟷ x ⊑ (:sfst⋅x, y:)"
  by (cases "x = ⊥", simp, cases "y = ⊥", simp, simp add: below_sprod)


subsection ‹Compactness›

lemma compact_sfst: "compact x ⟹ compact (sfst⋅x)"
  by (rule compactI) (simp add: sfst_below_iff)

lemma compact_ssnd: "compact x ⟹ compact (ssnd⋅x)"
  by (rule compactI) (simp add: ssnd_below_iff)

lemma compact_spair: "compact x ⟹ compact y ⟹ compact (:x, y:)"
  by (rule compact_sprod) (simp add: Rep_sprod_spair seq_conv_if)

lemma compact_spair_iff: "compact (:x, y:) ⟷ x = ⊥ ∨ y = ⊥ ∨ (compact x ∧ compact y)"
  apply (safe elim!: compact_spair)
     apply (drule compact_sfst, simp)
    apply (drule compact_ssnd, simp)
   apply simp
  apply simp
  done


subsection ‹Properties of \emph{ssplit}›

lemma ssplit1 [simp]: "ssplit⋅f⋅⊥ = ⊥"
  by (simp add: ssplit_def)

lemma ssplit2 [simp]: "x ≠ ⊥ ⟹ y ≠ ⊥ ⟹ ssplit⋅f⋅(:x, y:) = f⋅x⋅y"
  by (simp add: ssplit_def)

lemma ssplit3 [simp]: "ssplit⋅spair⋅z = z"
  by (cases z) simp_all


subsection ‹Strict product preserves flatness›

instance sprod :: (flat, flat) flat
proof
  fix x y :: "'a ⊗ 'b"
  assume "x ⊑ y"
  then show "x = ⊥ ∨ x = y"
    apply (induct x, simp)
    apply (induct y, simp)
    apply (simp add: spair_below_iff flat_below_iff)
    done
qed

end