Theory N_Relation_Algebras

(* Title:      N-Relation-Algebras
   Author:     Walter Guttmann
   Maintainer: Walter Guttmann <walter.guttmann at canterbury.ac.nz>
*)

section ‹N-Relation-Algebras›

theory N_Relation_Algebras

imports Stone_Relation_Algebras.Relation_Algebras N_Omega_Algebras

begin

context bounded_distrib_allegory
begin

subclass lattice_ordered_pre_left_semiring ..

end

text ‹Theorem 37›

sublocale relation_algebra < n_algebra where sup = sup and bot = bot and top = top and inf = inf and n = N and L = top
  apply unfold_locales
  using N_comp_top comp_inf.semiring.distrib_left inf.sup_monoid.add_commute inf_vector_comp apply simp
  apply (metis N_comp compl_sup double_compl mult_assoc mult_right_dist_sup top_mult_top N_comp_N)
  apply (metis brouwer.p_antitone inf.sup_monoid.add_commute inf.sup_right_isotone mult_left_isotone p_antitone_sup)
  apply simp
  using N_vector_top apply force
  apply simp
  apply (simp add: brouwer.p_antitone_iff top_right_mult_increasing)
  apply simp
  apply (metis N_comp_top conv_complement_sub double_compl le_supI2 le_iff_sup mult_assoc mult_left_isotone schroeder_3)
  by simp

sublocale relation_algebra < n_algebra_apx where sup = sup and bot = bot and top = top and inf = inf and n = N and L = top and apx = greater_eq
  apply unfold_locales
  using n_less_eq_char by force

no_notation
  inverse_divide (infixl "'/" 70)

notation
  divide (infixl "'/" 70)

class left_residuated_relation_algebra = relation_algebra + inverse +
  assumes lres_def: "x / y = -(-x * y⇧T)"
begin

text ‹Theorem 32.1›

subclass residuated_pre_left_semiring
  apply unfold_locales
  by (metis compl_le_swap1 lres_def schroeder_4)

end

context left_residuated_relation_algebra
begin

text ‹Theorem 32.3›

lemma lres_mult_lres_lres:
  "x / (z * y) = (x / y) / z"
  by (metis conv_dist_comp double_compl lres_def mult_assoc)

text ‹Theorem 32.5›

lemma lres_dist_inf:
  "(x ⊓ y) / z = (x / z) ⊓ (y / z)"
  by (metis compl_inf compl_sup lres_def mult_right_dist_sup)

text ‹Theorem 32.6›

lemma lres_add_export_vector:
  assumes "vector x"
    shows "(x ⊔ y) / z = x ⊔ (y / z)"
proof -
  have "(x ⊔ y) / z = -((-x ⊓ -y) * z⇧T)"
    by (simp add: lres_def)
  also have "... = -(-x ⊓ (-y * z⇧T))"
    using assms vector_complement_closed vector_inf_comp by auto
  also have "... = x ⊔ (y / z)"
    by (simp add: lres_def)
  finally show ?thesis
    .
qed

text ‹Theorem 32.7›

lemma lres_top_vector:
  "vector (x / top)"
  using equivalence_top_closed lres_def vector_complement_closed vector_mult_closed vector_top_closed by auto

text ‹Theorem 32.10›

lemma lres_top_export_inf_mult:
  "((x / top) ⊓ y) * z = (x / top) ⊓ (y * z)"
  by (simp add: vector_inf_comp lres_top_vector)

lemma N_lres:
  "N(x) = x / top ⊓ 1"
  using lres_def by auto

end

class complete_relation_algebra = relation_algebra + complete_lattice
begin

definition mu :: "('a ⇒ 'a) ⇒ 'a" where "mu f ≡ Inf { y . f y ≤ y }"
definition nu :: "('a ⇒ 'a) ⇒ 'a" where "nu f ≡ Sup { y . y ≤ f y }"

lemma mu_lower_bound:
  "f x ≤ x ⟹ mu f ≤ x"
  by (auto simp add: mu_def intro: Inf_lower)

lemma mu_greatest_lower_bound:
  "(∀y . f y ≤ y ⟶ x ≤ y) ⟹ x ≤ mu f"
  using lfp_def lfp_greatest mu_def by auto

lemma mu_unfold_1:
  "isotone f ⟹ f (mu f) ≤ mu f"
  by (metis mu_greatest_lower_bound order_trans mu_lower_bound isotone_def)

lemma mu_unfold_2:
  "isotone f ⟹ mu f ≤ f (mu f)"
  by (simp add: mu_lower_bound mu_unfold_1 ord.isotone_def)

lemma mu_unfold:
  "isotone f ⟹ mu f = f (mu f)"
  by (simp add: order.antisym mu_unfold_1 mu_unfold_2)

lemma mu_const:
  "mu (λx . y) = y"
  by (simp add: isotone_def mu_unfold)

lemma mu_lpfp:
  "isotone f ⟹ is_least_prefixpoint f (mu f)"
  by (simp add: is_least_prefixpoint_def mu_lower_bound mu_unfold_1)
  
lemma mu_lfp:
  "isotone f ⟹ is_least_fixpoint f (mu f)"
  by (metis is_least_fixpoint_def mu_lower_bound mu_unfold order_refl)

lemma mu_pmu:
  "isotone f ⟹ pμ f = mu f"
  using least_prefixpoint_same mu_lpfp by force
  
lemma mu_mu:
  "isotone f ⟹ μ f = mu f"
  using least_fixpoint_same mu_lfp by fastforce
  
end

class omega_relation_algebra = relation_algebra + star + omega +
  assumes ra_star_left_unfold : "1 ⊔ y * y⇧⋆ ≤ y⇧⋆"
  assumes ra_star_left_induct : "z ⊔ y * x ≤ x ⟶ y⇧⋆ * z ≤ x"
  assumes ra_star_right_induct: "z ⊔ x * y ≤ x ⟶ z * y⇧⋆ ≤ x"
  assumes ra_omega_unfold: "y⇧ω = y * y⇧ω"
  assumes ra_omega_induct: "x ≤ z ⊔ y * x ⟶ x ≤ y⇧ω ⊔ y⇧⋆ * z"
begin

subclass bounded_omega_algebra
  apply unfold_locales
  using ra_star_left_unfold apply blast
  using ra_star_left_induct apply blast
  using ra_star_right_induct apply blast
  using ra_omega_unfold apply blast
  using ra_omega_induct by blast

end

text ‹Theorem 38›

sublocale omega_relation_algebra < n_omega_algebra where sup = sup and bot = bot and top = top and inf = inf and n = N and L = top and apx = greater_eq and Omega = "λx . N(x⇧ω) * top ⊔ x⇧⋆"
  apply unfold_locales
  apply simp
  using n_split_omega_mult omega_vector star_mult_omega apply force
  by simp

end