# HG changeset patch
# User ballarin
# Date 1081842160 -7200
# Node ID 2cb6ff394bfbc915ceb0d91122622e1034c145c5
# Parent  b13da5649bf92796ab938f3f2eb332dd9c36f35f
Various changes to HOL-Algebra;
Locale instantiation.

diff -r b13da5649bf9 -r 2cb6ff394bfb NEWS
--- a/NEWS	Tue Apr 13 07:48:32 2004 +0200
+++ b/NEWS	Tue Apr 13 09:42:40 2004 +0200
@@ -85,13 +85,17 @@
   - Rule sets <locale>.intro and <locale>.axioms no longer declared as
     [intro?] and [elim?] (respectively) by default.
   - Experimental command for instantiation of locales in proof contexts:
-        instantiate <label>: <loc>
+        instantiate <label>[<attrs>]: <loc>
     Instantiates locale <loc> and adds all its theorems to the current context
-    taking into account their attributes, and qualifying their names with
-    <label>.  If the locale has assumptions, a chained fact of the form
+    taking into account their attributes.  Label and attrs are optional
+    modifiers, like in theorem declarations.  If present, names of
+    instantiated theorems are qualified with <label>, and the attributes
+    <attrs> are applied after any attributes these theorems might have already.
+      If the locale has assumptions, a chained fact of the form
     "<loc> t1 ... tn" is expected from which instantiations of the parameters
-    are derived.
-    A few (very simple) examples can be found in FOL/ex/LocaleInst.thy.
+    are derived.  The command does not support old-style locales declared
+    with "locale (open)".
+      A few (very simple) examples can be found in FOL/ex/LocaleInst.thy.
 
 * HOL: Tactic emulation methods induct_tac and case_tac understand static
   (Isar) contexts.
diff -r b13da5649bf9 -r 2cb6ff394bfb src/FOL/ex/LocaleInst.thy
--- a/src/FOL/ex/LocaleInst.thy	Tue Apr 13 07:48:32 2004 +0200
+++ b/src/FOL/ex/LocaleInst.thy	Tue Apr 13 09:42:40 2004 +0200
@@ -18,10 +18,18 @@
 
 lemma "[| A; B |] ==> A & B"
 proof -
-  instantiate my: L1   txt {* No chained fact required. *}
-  assume B and A  txt {* order reversed *}
+  instantiate my: L1           txt {* No chained fact required. *}
+  assume B and A               txt {* order reversed *}
+  then show "A & B" ..         txt {* Applies @{thm my.rev_conjI}. *}
+qed
+
+locale L11 = notes rev_conjI = conjI [THEN iffD1 [OF conj_commute]]
+
+lemma "[| A; B |] ==> A & B"
+proof -
+  instantiate [intro]: L11     txt {* Attribute supplied at instantiation. *}
+  assume B and A
   then show "A & B" ..
-  txt {* Applies @{thm my.rev_conjI}. *}
 qed
 
 section {* Simple locale with assumptions *}
@@ -111,4 +119,15 @@
   show ?thesis by (rule lem)  (* lem instantiated to True *)
 qed
 
+section {* Instantiation in a context with target *}
+
+lemma (in L4)  (* Target might confuse instantiation command. *)
+  fixes A (infixl "$" 60)
+  assumes A: "L4(A)"
+  shows "(x::i) $ y $ z $ w = y $ x $ w $ z"
+proof -
+  from A instantiate A: L4
+  show ?thesis by (simp only: A.OP.AC)
+qed
+
 end
diff -r b13da5649bf9 -r 2cb6ff394bfb src/HOL/Algebra/CRing.thy
--- a/src/HOL/Algebra/CRing.thy	Tue Apr 13 07:48:32 2004 +0200
+++ b/src/HOL/Algebra/CRing.thy	Tue Apr 13 09:42:40 2004 +0200
@@ -302,6 +302,9 @@
     and integral: "[| a \<otimes> b = \<zero>; a \<in> carrier R; b \<in> carrier R |] ==>
                   a = \<zero> | b = \<zero>"
 
+locale field = "domain" +
+  assumes field_Units: "Units R = carrier R - {\<zero>}"
+
 subsection {* Basic Facts of Rings *}
 
 lemma ringI:
@@ -357,7 +360,7 @@
   "comm_monoid R"
   by (auto intro!: comm_monoidI m_assoc m_comm)
 
-subsection {* Normaliser for Commutative Rings *}
+subsection {* Normaliser for Rings *}
 
 lemma (in abelian_group) r_neg2:
   "[| x \<in> carrier G; y \<in> carrier G |] ==> x \<oplus> (\<ominus> x \<oplus> y) = y"
diff -r b13da5649bf9 -r 2cb6ff394bfb src/HOL/Algebra/Group.thy
--- a/src/HOL/Algebra/Group.thy	Tue Apr 13 07:48:32 2004 +0200
+++ b/src/HOL/Algebra/Group.thy	Tue Apr 13 09:42:40 2004 +0200
@@ -410,6 +410,7 @@
   shows "semigroup (G(| carrier := H |))"
   using prems by fast
 
+
 locale subgroup = submagma H G +
   assumes one_closed [intro, simp]: "\<one> \<in> H"
     and m_inv_closed [intro, simp]: "x \<in> H ==> inv x \<in> H"
diff -r b13da5649bf9 -r 2cb6ff394bfb src/HOL/Algebra/Lattice.thy
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/HOL/Algebra/Lattice.thy	Tue Apr 13 09:42:40 2004 +0200
@@ -0,0 +1,985 @@
+(*
+  Title:     Orders and Lattices
+  Id:        $Id$
+  Author:    Clemens Ballarin, started 7 November 2003
+  Copyright: Clemens Ballarin
+*)
+
+theory Lattice = Group:
+
+section {* Order and Lattices *}
+
+subsection {* Partial Orders *}
+
+record 'a order = "'a partial_object" +
+  le :: "['a, 'a] => bool" (infixl "\<sqsubseteq>\<index>" 50)
+
+locale order_syntax = struct L
+
+locale partial_order = order_syntax +
+  assumes refl [intro, simp]:
+                  "x \<in> carrier L ==> x \<sqsubseteq> x"
+    and anti_sym [intro]:
+                  "[| x \<sqsubseteq> y; y \<sqsubseteq> x; x \<in> carrier L; y \<in> carrier L |] ==> x = y"
+    and trans [trans]:
+                  "[| x \<sqsubseteq> y; y \<sqsubseteq> z;
+                   x \<in> carrier L; y \<in> carrier L; z \<in> carrier L |] ==> x \<sqsubseteq> z"
+
+constdefs
+  less :: "[('a, 'm) order_scheme, 'a, 'a] => bool" (infixl "\<sqsubset>\<index>" 50)
+  "less L x y == le L x y & x ~= y"
+
+  (* Upper and lower bounds of a set. *)
+  Upper :: "[('a, 'm) order_scheme, 'a set] => 'a set"
+  "Upper L A == {u. (ALL x. x \<in> A \<inter> carrier L --> le L x u)} \<inter>
+                carrier L"
+
+  Lower :: "[('a, 'm) order_scheme, 'a set] => 'a set"
+  "Lower L A == {l. (ALL x. x \<in> A \<inter> carrier L --> le L l x)} \<inter>
+                carrier L"
+
+  (* Least and greatest, as predicate. *)
+  least :: "[('a, 'm) order_scheme, 'a, 'a set] => bool"
+  "least L l A == A \<subseteq> carrier L & l \<in> A & (ALL x : A. le L l x)"
+
+  greatest :: "[('a, 'm) order_scheme, 'a, 'a set] => bool"
+  "greatest L g A == A \<subseteq> carrier L & g \<in> A & (ALL x : A. le L x g)"
+
+  (* Supremum and infimum *)
+  sup :: "[('a, 'm) order_scheme, 'a set] => 'a" ("\<Squnion>\<index>_" [90] 90)
+  "sup L A == THE x. least L x (Upper L A)"
+
+  inf :: "[('a, 'm) order_scheme, 'a set] => 'a" ("\<Sqinter>\<index>_" [90] 90)
+  "inf L A == THE x. greatest L x (Lower L A)"
+
+  join :: "[('a, 'm) order_scheme, 'a, 'a] => 'a" (infixl "\<squnion>\<index>" 65)
+  "join L x y == sup L {x, y}"
+
+  meet :: "[('a, 'm) order_scheme, 'a, 'a] => 'a" (infixl "\<sqinter>\<index>" 65)
+  "meet L x y == inf L {x, y}"
+
+(* Upper *)
+
+lemma Upper_closed [intro, simp]:
+  "Upper L A \<subseteq> carrier L"
+  by (unfold Upper_def) clarify
+
+lemma UpperD [dest]:
+  includes order_syntax
+  shows "[| u \<in> Upper L A; x \<in> A; A \<subseteq> carrier L |] ==> x \<sqsubseteq> u"
+  by (unfold Upper_def) blast 
+
+lemma Upper_memI:
+  includes order_syntax
+  shows "[| !! y. y \<in> A ==> y \<sqsubseteq> x; x \<in> carrier L |] ==> x \<in> Upper L A"
+  by (unfold Upper_def) blast 
+
+lemma Upper_antimono:
+  "A \<subseteq> B ==> Upper L B \<subseteq> Upper L A"
+  by (unfold Upper_def) blast
+
+(* Lower *)
+
+lemma Lower_closed [intro, simp]:
+  "Lower L A \<subseteq> carrier L"
+  by (unfold Lower_def) clarify
+
+lemma LowerD [dest]:
+  includes order_syntax
+  shows "[| l \<in> Lower L A; x \<in> A; A \<subseteq> carrier L |] ==> l \<sqsubseteq> x"
+  by (unfold Lower_def) blast 
+
+lemma Lower_memI:
+  includes order_syntax
+  shows "[| !! y. y \<in> A ==> x \<sqsubseteq> y; x \<in> carrier L |] ==> x \<in> Lower L A"
+  by (unfold Lower_def) blast 
+
+lemma Lower_antimono:
+  "A \<subseteq> B ==> Lower L B \<subseteq> Lower L A"
+  by (unfold Lower_def) blast
+
+(* least *)
+
+lemma least_carrier [intro, simp]:
+  shows "least L l A ==> l \<in> carrier L"
+  by (unfold least_def) fast
+
+lemma least_mem:
+  "least L l A ==> l \<in> A"
+  by (unfold least_def) fast
+
+lemma (in partial_order) least_unique:
+  "[| least L x A; least L y A |] ==> x = y"
+  by (unfold least_def) blast
+
+lemma least_le:
+  includes order_syntax
+  shows "[| least L x A; a \<in> A |] ==> x \<sqsubseteq> a"
+  by (unfold least_def) fast
+
+lemma least_UpperI:
+  includes order_syntax
+  assumes above: "!! x. x \<in> A ==> x \<sqsubseteq> s"
+    and below: "!! y. y \<in> Upper L A ==> s \<sqsubseteq> y"
+    and L: "A \<subseteq> carrier L" "s \<in> carrier L"
+  shows "least L s (Upper L A)"
+proof (unfold least_def, intro conjI)
+  show "Upper L A \<subseteq> carrier L" by simp
+next
+  from above L show "s \<in> Upper L A" by (simp add: Upper_def)
+next
+  from below show "ALL x : Upper L A. s \<sqsubseteq> x" by fast
+qed
+
+(* greatest *)
+
+lemma greatest_carrier [intro, simp]:
+  shows "greatest L l A ==> l \<in> carrier L"
+  by (unfold greatest_def) fast
+
+lemma greatest_mem:
+  "greatest L l A ==> l \<in> A"
+  by (unfold greatest_def) fast
+
+lemma (in partial_order) greatest_unique:
+  "[| greatest L x A; greatest L y A |] ==> x = y"
+  by (unfold greatest_def) blast
+
+lemma greatest_le:
+  includes order_syntax
+  shows "[| greatest L x A; a \<in> A |] ==> a \<sqsubseteq> x"
+  by (unfold greatest_def) fast
+
+lemma greatest_LowerI:
+  includes order_syntax
+  assumes below: "!! x. x \<in> A ==> i \<sqsubseteq> x"
+    and above: "!! y. y \<in> Lower L A ==> y \<sqsubseteq> i"
+    and L: "A \<subseteq> carrier L" "i \<in> carrier L"
+  shows "greatest L i (Lower L A)"
+proof (unfold greatest_def, intro conjI)
+  show "Lower L A \<subseteq> carrier L" by simp
+next
+  from below L show "i \<in> Lower L A" by (simp add: Lower_def)
+next
+  from above show "ALL x : Lower L A. x \<sqsubseteq> i" by fast
+qed
+
+subsection {* Lattices *}
+
+locale lattice = partial_order +
+  assumes sup_of_two_exists:
+    "[| x \<in> carrier L; y \<in> carrier L |] ==> EX s. least L s (Upper L {x, y})"
+    and inf_of_two_exists:
+    "[| x \<in> carrier L; y \<in> carrier L |] ==> EX s. greatest L s (Lower L {x, y})"
+
+lemma least_Upper_above:
+  includes order_syntax
+  shows "[| least L s (Upper L A); x \<in> A; A \<subseteq> carrier L |] ==> x \<sqsubseteq> s"
+  by (unfold least_def) blast
+
+lemma greatest_Lower_above:
+  includes order_syntax
+  shows "[| greatest L i (Lower L A); x \<in> A; A \<subseteq> carrier L |] ==> i \<sqsubseteq> x"
+  by (unfold greatest_def) blast
+
+subsubsection {* Supremum *}
+
+lemma (in lattice) joinI:
+  "[| !!l. least L l (Upper L {x, y}) ==> P l; x \<in> carrier L; y \<in> carrier L |]
+  ==> P (x \<squnion> y)"
+proof (unfold join_def sup_def)
+  assume L: "x \<in> carrier L" "y \<in> carrier L"
+    and P: "!!l. least L l (Upper L {x, y}) ==> P l"
+  with sup_of_two_exists obtain s where "least L s (Upper L {x, y})" by fast
+  with L show "P (THE l. least L l (Upper L {x, y}))"
+  by (fast intro: theI2 least_unique P)
+qed
+
+lemma (in lattice) join_closed [simp]:
+  "[| x \<in> carrier L; y \<in> carrier L |] ==> x \<squnion> y \<in> carrier L"
+  by (rule joinI) (rule least_carrier)
+
+lemma (in partial_order) sup_of_singletonI:
+  (* only reflexivity needed ? *)
+  "x \<in> carrier L ==> least L x (Upper L {x})"
+  by (rule least_UpperI) fast+
+
+lemma (in partial_order) sup_of_singleton [simp]:
+  includes order_syntax
+  shows "x \<in> carrier L ==> \<Squnion> {x} = x"
+  by (unfold sup_def) (blast intro: least_unique least_UpperI sup_of_singletonI)
+
+text {* Condition on A: supremum exists. *}
+
+lemma (in lattice) sup_insertI:
+  "[| !!s. least L s (Upper L (insert x A)) ==> P s;
+  least L a (Upper L A); x \<in> carrier L; A \<subseteq> carrier L |]
+  ==> P (\<Squnion> (insert x A))"
+proof (unfold sup_def)
+  assume L: "x \<in> carrier L" "A \<subseteq> carrier L"
+    and P: "!!l. least L l (Upper L (insert x A)) ==> P l"
+    and least_a: "least L a (Upper L A)"
+  from L least_a have La: "a \<in> carrier L" by simp
+  from L sup_of_two_exists least_a
+  obtain s where least_s: "least L s (Upper L {a, x})" by blast
+  show "P (THE l. least L l (Upper L (insert x A)))"
+  proof (rule theI2 [where a = s])
+    show "least L s (Upper L (insert x A))"
+    proof (rule least_UpperI)
+      fix z
+      assume xA: "z \<in> insert x A"
+      show "z \<sqsubseteq> s"
+      proof -
+	{
+	  assume "z = x" then have ?thesis
+	    by (simp add: least_Upper_above [OF least_s] L La)
+        }
+	moreover
+        {
+	  assume "z \<in> A"
+          with L least_s least_a have ?thesis
+	    by (rule_tac trans [where y = a]) (auto dest: least_Upper_above)
+        }
+      moreover note xA
+      ultimately show ?thesis by blast
+    qed
+  next
+    fix y
+    assume y: "y \<in> Upper L (insert x A)"
+    show "s \<sqsubseteq> y"
+    proof (rule least_le [OF least_s], rule Upper_memI)
+      fix z
+      assume z: "z \<in> {a, x}"
+      show "z \<sqsubseteq> y"
+      proof -
+	{
+          have y': "y \<in> Upper L A"
+	    apply (rule subsetD [where A = "Upper L (insert x A)"])
+	    apply (rule Upper_antimono) apply clarify apply assumption
+	    done
+	  assume "z = a"
+	  with y' least_a have ?thesis by (fast dest: least_le)
+        }
+	moreover
+	{
+           assume "z = x"
+           with y L have ?thesis by blast
+        }
+        moreover note z
+        ultimately show ?thesis by blast
+      qed
+    qed (rule Upper_closed [THEN subsetD])
+  next
+    from L show "insert x A \<subseteq> carrier L" by simp
+  next
+    from least_s show "s \<in> carrier L" by simp
+  qed
+next
+    fix l
+    assume least_l: "least L l (Upper L (insert x A))"
+    show "l = s"
+    proof (rule least_unique)
+      show "least L s (Upper L (insert x A))"
+      proof (rule least_UpperI)
+	fix z
+	assume xA: "z \<in> insert x A"
+	show "z \<sqsubseteq> s"
+      proof -
+	{
+	  assume "z = x" then have ?thesis
+	    by (simp add: least_Upper_above [OF least_s] L La)
+        }
+	moreover
+        {
+	  assume "z \<in> A"
+          with L least_s least_a have ?thesis
+	    by (rule_tac trans [where y = a]) (auto dest: least_Upper_above)
+        }
+	  moreover note xA
+	  ultimately show ?thesis by blast
+	qed
+      next
+	fix y
+	assume y: "y \<in> Upper L (insert x A)"
+	show "s \<sqsubseteq> y"
+	proof (rule least_le [OF least_s], rule Upper_memI)
+	  fix z
+	  assume z: "z \<in> {a, x}"
+	  show "z \<sqsubseteq> y"
+	  proof -
+	    {
+          have y': "y \<in> Upper L A"
+	    apply (rule subsetD [where A = "Upper L (insert x A)"])
+	    apply (rule Upper_antimono) apply clarify apply assumption
+	    done
+	  assume "z = a"
+	  with y' least_a have ?thesis by (fast dest: least_le)
+        }
+	moreover
+	{
+           assume "z = x"
+           with y L have ?thesis by blast
+            }
+            moreover note z
+            ultimately show ?thesis by blast
+	  qed
+	qed (rule Upper_closed [THEN subsetD])
+      next
+	from L show "insert x A \<subseteq> carrier L" by simp
+      next
+	from least_s show "s \<in> carrier L" by simp
+      qed
+    qed
+  qed
+qed
+
+lemma (in lattice) finite_sup_least:
+  "[| finite A; A \<subseteq> carrier L; A ~= {} |] ==> least L (\<Squnion> A) (Upper L A)"
+proof (induct set: Finites)
+  case empty then show ?case by simp
+next
+  case (insert A x)
+  show ?case
+  proof (cases "A = {}")
+    case True
+    with insert show ?thesis by (simp add: sup_of_singletonI)
+  next
+    case False
+    from insert show ?thesis
+    proof (rule_tac sup_insertI)
+      from False insert show "least L (\<Squnion> A) (Upper L A)" by simp
+    qed simp_all
+  qed
+qed
+
+lemma (in lattice) finite_sup_insertI:
+  assumes P: "!!l. least L l (Upper L (insert x A)) ==> P l"
+    and xA: "finite A" "x \<in> carrier L" "A \<subseteq> carrier L"
+  shows "P (\<Squnion> (insert x A))"
+proof (cases "A = {}")
+  case True with P and xA show ?thesis
+    by (simp add: sup_of_singletonI)
+next
+  case False with P and xA show ?thesis
+    by (simp add: sup_insertI finite_sup_least)
+qed
+
+lemma (in lattice) finite_sup_closed:
+  "[| finite A; A \<subseteq> carrier L; A ~= {} |] ==> \<Squnion> A \<in> carrier L"
+proof (induct set: Finites)
+  case empty then show ?case by simp
+next
+  case (insert A x) then show ?case
+    by (rule_tac finite_sup_insertI) (simp_all)
+qed
+
+lemma (in lattice) join_left:
+  "[| x \<in> carrier L; y \<in> carrier L |] ==> x \<sqsubseteq> x \<squnion> y"
+  by (rule joinI [folded join_def]) (blast dest: least_mem )
+
+lemma (in lattice) join_right:
+  "[| x \<in> carrier L; y \<in> carrier L |] ==> y \<sqsubseteq> x \<squnion> y"
+  by (rule joinI [folded join_def]) (blast dest: least_mem )
+
+lemma (in lattice) sup_of_two_least:
+  "[| x \<in> carrier L; y \<in> carrier L |] ==> least L (\<Squnion> {x, y}) (Upper L {x, y})"
+proof (unfold sup_def)
+  assume L: "x \<in> carrier L" "y \<in> carrier L"
+  with sup_of_two_exists obtain s where "least L s (Upper L {x, y})" by fast
+  with L show "least L (THE xa. least L xa (Upper L {x, y})) (Upper L {x, y})"
+  by (fast intro: theI2 least_unique)  (* blast fails *)
+qed
+
+lemma (in lattice) join_le:
+  assumes sub: "x \<sqsubseteq> z" "y \<sqsubseteq> z"
+    and L: "x \<in> carrier L" "y \<in> carrier L" "z \<in> carrier L"
+  shows "x \<squnion> y \<sqsubseteq> z"
+proof (rule joinI)
+  fix s
+  assume "least L s (Upper L {x, y})"
+  with sub L show "s \<sqsubseteq> z" by (fast elim: least_le intro: Upper_memI)
+qed
+  
+lemma (in lattice) join_assoc_lemma:
+  assumes L: "x \<in> carrier L" "y \<in> carrier L" "z \<in> carrier L"
+  shows "x \<squnion> (y \<squnion> z) = \<Squnion> {x, y, z}"
+proof (rule finite_sup_insertI)
+  (* The textbook argument in Jacobson I, p 457 *)
+  fix s
+  assume sup: "least L s (Upper L {x, y, z})"
+  show "x \<squnion> (y \<squnion> z) = s"
+  proof (rule anti_sym)
+    from sup L show "x \<squnion> (y \<squnion> z) \<sqsubseteq> s"
+      by (fastsimp intro!: join_le elim: least_Upper_above)
+  next
+    from sup L show "s \<sqsubseteq> x \<squnion> (y \<squnion> z)"
+    by (erule_tac least_le)
+      (blast intro!: Upper_memI intro: trans join_left join_right join_closed)
+  qed (simp_all add: L least_carrier [OF sup])
+qed (simp_all add: L)
+
+lemma join_comm:
+  includes order_syntax
+  shows "x \<squnion> y = y \<squnion> x"
+  by (unfold join_def) (simp add: insert_commute)
+
+lemma (in lattice) join_assoc:
+  assumes L: "x \<in> carrier L" "y \<in> carrier L" "z \<in> carrier L"
+  shows "(x \<squnion> y) \<squnion> z = x \<squnion> (y \<squnion> z)"
+proof -
+  have "(x \<squnion> y) \<squnion> z = z \<squnion> (x \<squnion> y)" by (simp only: join_comm)
+  also from L have "... = \<Squnion> {z, x, y}" by (simp add: join_assoc_lemma)
+  also from L have "... = \<Squnion> {x, y, z}" by (simp add: insert_commute)
+  also from L have "... = x \<squnion> (y \<squnion> z)" by (simp add: join_assoc_lemma)
+  finally show ?thesis .
+qed
+
+subsubsection {* Infimum *}
+
+lemma (in lattice) meetI:
+  "[| !!i. greatest L i (Lower L {x, y}) ==> P i;
+  x \<in> carrier L; y \<in> carrier L |]
+  ==> P (x \<sqinter> y)"
+proof (unfold meet_def inf_def)
+  assume L: "x \<in> carrier L" "y \<in> carrier L"
+    and P: "!!g. greatest L g (Lower L {x, y}) ==> P g"
+  with inf_of_two_exists obtain i where "greatest L i (Lower L {x, y})" by fast
+  with L show "P (THE g. greatest L g (Lower L {x, y}))"
+  by (fast intro: theI2 greatest_unique P)
+qed
+
+lemma (in lattice) meet_closed [simp]:
+  "[| x \<in> carrier L; y \<in> carrier L |] ==> x \<sqinter> y \<in> carrier L"
+  by (rule meetI) (rule greatest_carrier)
+
+lemma (in partial_order) inf_of_singletonI:
+  (* only reflexivity needed ? *)
+  "x \<in> carrier L ==> greatest L x (Lower L {x})"
+  by (rule greatest_LowerI) fast+
+
+lemma (in partial_order) inf_of_singleton [simp]:
+  includes order_syntax
+  shows "x \<in> carrier L ==> \<Sqinter> {x} = x"
+  by (unfold inf_def) (blast intro: greatest_unique greatest_LowerI inf_of_singletonI)
+
+text {* Condition on A: infimum exists. *}
+
+lemma (in lattice) inf_insertI:
+  "[| !!i. greatest L i (Lower L (insert x A)) ==> P i;
+  greatest L a (Lower L A); x \<in> carrier L; A \<subseteq> carrier L |]
+  ==> P (\<Sqinter> (insert x A))"
+proof (unfold inf_def)
+  assume L: "x \<in> carrier L" "A \<subseteq> carrier L"
+    and P: "!!g. greatest L g (Lower L (insert x A)) ==> P g"
+    and greatest_a: "greatest L a (Lower L A)"
+  from L greatest_a have La: "a \<in> carrier L" by simp
+  from L inf_of_two_exists greatest_a
+  obtain i where greatest_i: "greatest L i (Lower L {a, x})" by blast
+  show "P (THE g. greatest L g (Lower L (insert x A)))"
+  proof (rule theI2 [where a = i])
+    show "greatest L i (Lower L (insert x A))"
+    proof (rule greatest_LowerI)
+      fix z
+      assume xA: "z \<in> insert x A"
+      show "i \<sqsubseteq> z"
+      proof -
+	{
+	  assume "z = x" then have ?thesis
+	    by (simp add: greatest_Lower_above [OF greatest_i] L La)
+        }
+	moreover
+        {
+	  assume "z \<in> A"
+          with L greatest_i greatest_a have ?thesis
+	    by (rule_tac trans [where y = a]) (auto dest: greatest_Lower_above)
+        }
+      moreover note xA
+      ultimately show ?thesis by blast
+    qed
+  next
+    fix y
+    assume y: "y \<in> Lower L (insert x A)"
+    show "y \<sqsubseteq> i"
+    proof (rule greatest_le [OF greatest_i], rule Lower_memI)
+      fix z
+      assume z: "z \<in> {a, x}"
+      show "y \<sqsubseteq> z"
+      proof -
+	{
+          have y': "y \<in> Lower L A"
+	    apply (rule subsetD [where A = "Lower L (insert x A)"])
+	    apply (rule Lower_antimono) apply clarify apply assumption
+	    done
+	  assume "z = a"
+	  with y' greatest_a have ?thesis by (fast dest: greatest_le)
+        }
+	moreover
+	{
+           assume "z = x"
+           with y L have ?thesis by blast
+        }
+        moreover note z
+        ultimately show ?thesis by blast
+      qed
+    qed (rule Lower_closed [THEN subsetD])
+  next
+    from L show "insert x A \<subseteq> carrier L" by simp
+  next
+    from greatest_i show "i \<in> carrier L" by simp
+  qed
+next
+    fix g
+    assume greatest_g: "greatest L g (Lower L (insert x A))"
+    show "g = i"
+    proof (rule greatest_unique)
+      show "greatest L i (Lower L (insert x A))"
+      proof (rule greatest_LowerI)
+	fix z
+	assume xA: "z \<in> insert x A"
+	show "i \<sqsubseteq> z"
+      proof -
+	{
+	  assume "z = x" then have ?thesis
+	    by (simp add: greatest_Lower_above [OF greatest_i] L La)
+        }
+	moreover
+        {
+	  assume "z \<in> A"
+          with L greatest_i greatest_a have ?thesis
+	    by (rule_tac trans [where y = a]) (auto dest: greatest_Lower_above)
+        }
+	  moreover note xA
+	  ultimately show ?thesis by blast
+	qed
+      next
+	fix y
+	assume y: "y \<in> Lower L (insert x A)"
+	show "y \<sqsubseteq> i"
+	proof (rule greatest_le [OF greatest_i], rule Lower_memI)
+	  fix z
+	  assume z: "z \<in> {a, x}"
+	  show "y \<sqsubseteq> z"
+	  proof -
+	    {
+          have y': "y \<in> Lower L A"
+	    apply (rule subsetD [where A = "Lower L (insert x A)"])
+	    apply (rule Lower_antimono) apply clarify apply assumption
+	    done
+	  assume "z = a"
+	  with y' greatest_a have ?thesis by (fast dest: greatest_le)
+        }
+	moreover
+	{
+           assume "z = x"
+           with y L have ?thesis by blast
+            }
+            moreover note z
+            ultimately show ?thesis by blast
+	  qed
+	qed (rule Lower_closed [THEN subsetD])
+      next
+	from L show "insert x A \<subseteq> carrier L" by simp
+      next
+	from greatest_i show "i \<in> carrier L" by simp
+      qed
+    qed
+  qed
+qed
+
+lemma (in lattice) finite_inf_greatest:
+  "[| finite A; A \<subseteq> carrier L; A ~= {} |] ==> greatest L (\<Sqinter> A) (Lower L A)"
+proof (induct set: Finites)
+  case empty then show ?case by simp
+next
+  case (insert A x)
+  show ?case
+  proof (cases "A = {}")
+    case True
+    with insert show ?thesis by (simp add: inf_of_singletonI)
+  next
+    case False
+    from insert show ?thesis
+    proof (rule_tac inf_insertI)
+      from False insert show "greatest L (\<Sqinter> A) (Lower L A)" by simp
+    qed simp_all
+  qed
+qed
+
+lemma (in lattice) finite_inf_insertI:
+  assumes P: "!!i. greatest L i (Lower L (insert x A)) ==> P i"
+    and xA: "finite A" "x \<in> carrier L" "A \<subseteq> carrier L"
+  shows "P (\<Sqinter> (insert x A))"
+proof (cases "A = {}")
+  case True with P and xA show ?thesis
+    by (simp add: inf_of_singletonI)
+next
+  case False with P and xA show ?thesis
+    by (simp add: inf_insertI finite_inf_greatest)
+qed
+
+lemma (in lattice) finite_inf_closed:
+  "[| finite A; A \<subseteq> carrier L; A ~= {} |] ==> \<Sqinter> A \<in> carrier L"
+proof (induct set: Finites)
+  case empty then show ?case by simp
+next
+  case (insert A x) then show ?case
+    by (rule_tac finite_inf_insertI) (simp_all)
+qed
+
+lemma (in lattice) meet_left:
+  "[| x \<in> carrier L; y \<in> carrier L |] ==> x \<sqinter> y \<sqsubseteq> x"
+  by (rule meetI [folded meet_def]) (blast dest: greatest_mem )
+
+lemma (in lattice) meet_right:
+  "[| x \<in> carrier L; y \<in> carrier L |] ==> x \<sqinter> y \<sqsubseteq> y"
+  by (rule meetI [folded meet_def]) (blast dest: greatest_mem )
+
+lemma (in lattice) inf_of_two_greatest:
+  "[| x \<in> carrier L; y \<in> carrier L |] ==>
+  greatest L (\<Sqinter> {x, y}) (Lower L {x, y})"
+proof (unfold inf_def)
+  assume L: "x \<in> carrier L" "y \<in> carrier L"
+  with inf_of_two_exists obtain s where "greatest L s (Lower L {x, y})" by fast
+  with L
+  show "greatest L (THE xa. greatest L xa (Lower L {x, y})) (Lower L {x, y})"
+  by (fast intro: theI2 greatest_unique)  (* blast fails *)
+qed
+
+lemma (in lattice) meet_le:
+  assumes sub: "z \<sqsubseteq> x" "z \<sqsubseteq> y"
+    and L: "x \<in> carrier L" "y \<in> carrier L" "z \<in> carrier L"
+  shows "z \<sqsubseteq> x \<sqinter> y"
+proof (rule meetI)
+  fix i
+  assume "greatest L i (Lower L {x, y})"
+  with sub L show "z \<sqsubseteq> i" by (fast elim: greatest_le intro: Lower_memI)
+qed
+  
+lemma (in lattice) meet_assoc_lemma:
+  assumes L: "x \<in> carrier L" "y \<in> carrier L" "z \<in> carrier L"
+  shows "x \<sqinter> (y \<sqinter> z) = \<Sqinter> {x, y, z}"
+proof (rule finite_inf_insertI)
+  txt {* The textbook argument in Jacobson I, p 457 *}
+  fix i
+  assume inf: "greatest L i (Lower L {x, y, z})"
+  show "x \<sqinter> (y \<sqinter> z) = i"
+  proof (rule anti_sym)
+    from inf L show "i \<sqsubseteq> x \<sqinter> (y \<sqinter> z)"
+      by (fastsimp intro!: meet_le elim: greatest_Lower_above)
+  next
+    from inf L show "x \<sqinter> (y \<sqinter> z) \<sqsubseteq> i"
+    by (erule_tac greatest_le)
+      (blast intro!: Lower_memI intro: trans meet_left meet_right meet_closed)
+  qed (simp_all add: L greatest_carrier [OF inf])
+qed (simp_all add: L)
+
+lemma meet_comm:
+  includes order_syntax
+  shows "x \<sqinter> y = y \<sqinter> x"
+  by (unfold meet_def) (simp add: insert_commute)
+
+lemma (in lattice) meet_assoc:
+  assumes L: "x \<in> carrier L" "y \<in> carrier L" "z \<in> carrier L"
+  shows "(x \<sqinter> y) \<sqinter> z = x \<sqinter> (y \<sqinter> z)"
+proof -
+  have "(x \<sqinter> y) \<sqinter> z = z \<sqinter> (x \<sqinter> y)" by (simp only: meet_comm)
+  also from L have "... = \<Sqinter> {z, x, y}" by (simp add: meet_assoc_lemma)
+  also from L have "... = \<Sqinter> {x, y, z}" by (simp add: insert_commute)
+  also from L have "... = x \<sqinter> (y \<sqinter> z)" by (simp add: meet_assoc_lemma)
+  finally show ?thesis .
+qed
+
+subsection {* Total Orders *}
+
+locale total_order = lattice +
+  assumes total: "[| x \<in> carrier L; y \<in> carrier L |] ==> x \<sqsubseteq> y | y \<sqsubseteq> x"
+
+text {* Introduction rule: the usual definition of total order *}
+
+lemma (in partial_order) total_orderI:
+  assumes total: "!!x y. [| x \<in> carrier L; y \<in> carrier L |] ==> x \<sqsubseteq> y | y \<sqsubseteq> x"
+  shows "total_order L"
+proof (rule total_order.intro)
+  show "lattice_axioms L"
+  proof (rule lattice_axioms.intro)
+    fix x y
+    assume L: "x \<in> carrier L" "y \<in> carrier L"
+    show "EX s. least L s (Upper L {x, y})"
+    proof -
+      note total L
+      moreover
+      {
+	assume "x \<sqsubseteq> y"
+        with L have "least L y (Upper L {x, y})"
+	  by (rule_tac least_UpperI) auto
+      }
+      moreover
+      {
+	assume "y \<sqsubseteq> x"
+        with L have "least L x (Upper L {x, y})"
+	  by (rule_tac least_UpperI) auto
+      }
+      ultimately show ?thesis by blast
+    qed
+  next
+    fix x y
+    assume L: "x \<in> carrier L" "y \<in> carrier L"
+    show "EX i. greatest L i (Lower L {x, y})"
+    proof -
+      note total L
+      moreover
+      {
+	assume "y \<sqsubseteq> x"
+        with L have "greatest L y (Lower L {x, y})"
+	  by (rule_tac greatest_LowerI) auto
+      }
+      moreover
+      {
+	assume "x \<sqsubseteq> y"
+        with L have "greatest L x (Lower L {x, y})"
+	  by (rule_tac greatest_LowerI) auto
+      }
+      ultimately show ?thesis by blast
+    qed
+  qed
+qed (assumption | rule total_order_axioms.intro)+
+
+subsection {* Complete lattices *}
+
+locale complete_lattice = lattice +
+  assumes sup_exists:
+    "[| A \<subseteq> carrier L |] ==> EX s. least L s (Upper L A)"
+    and inf_exists:
+    "[| A \<subseteq> carrier L |] ==> EX i. greatest L i (Lower L A)"
+
+text {* Introduction rule: the usual definition of complete lattice *}
+
+lemma (in partial_order) complete_latticeI:
+  assumes sup_exists:
+    "!!A. [| A \<subseteq> carrier L |] ==> EX s. least L s (Upper L A)"
+    and inf_exists:
+    "!!A. [| A \<subseteq> carrier L |] ==> EX i. greatest L i (Lower L A)"
+  shows "complete_lattice L"
+proof (rule complete_lattice.intro)
+  show "lattice_axioms L"
+  by (rule lattice_axioms.intro) (blast intro: sup_exists inf_exists)+
+qed (assumption | rule complete_lattice_axioms.intro)+
+
+constdefs
+  top :: "('a, 'm) order_scheme => 'a" ("\<top>\<index>")
+  "top L == sup L (carrier L)"
+
+  bottom :: "('a, 'm) order_scheme => 'a" ("\<bottom>\<index>")
+  "bottom L == inf L (carrier L)"
+
+
+lemma (in complete_lattice) supI:
+  "[| !!l. least L l (Upper L A) ==> P l; A \<subseteq> carrier L |]
+  ==> P (\<Squnion> A)"
+proof (unfold sup_def)
+  assume L: "A \<subseteq> carrier L"
+    and P: "!!l. least L l (Upper L A) ==> P l"
+  with sup_exists obtain s where "least L s (Upper L A)" by blast
+  with L show "P (THE l. least L l (Upper L A))"
+  by (fast intro: theI2 least_unique P)
+qed
+
+lemma (in complete_lattice) sup_closed [simp]:
+  "A \<subseteq> carrier L ==> \<Squnion> A \<in> carrier L"
+  by (rule supI) simp_all
+
+lemma (in complete_lattice) top_closed [simp, intro]:
+  "\<top> \<in> carrier L"
+  by (unfold top_def) simp
+
+lemma (in complete_lattice) infI:
+  "[| !!i. greatest L i (Lower L A) ==> P i; A \<subseteq> carrier L |]
+  ==> P (\<Sqinter> A)"
+proof (unfold inf_def)
+  assume L: "A \<subseteq> carrier L"
+    and P: "!!l. greatest L l (Lower L A) ==> P l"
+  with inf_exists obtain s where "greatest L s (Lower L A)" by blast
+  with L show "P (THE l. greatest L l (Lower L A))"
+  by (fast intro: theI2 greatest_unique P)
+qed
+
+lemma (in complete_lattice) inf_closed [simp]:
+  "A \<subseteq> carrier L ==> \<Sqinter> A \<in> carrier L"
+  by (rule infI) simp_all
+
+lemma (in complete_lattice) bottom_closed [simp, intro]:
+  "\<bottom> \<in> carrier L"
+  by (unfold bottom_def) simp
+
+text {* Jacobson: Theorem 8.1 *}
+
+lemma Lower_empty [simp]:
+  "Lower L {} = carrier L"
+  by (unfold Lower_def) simp
+
+lemma Upper_empty [simp]:
+  "Upper L {} = carrier L"
+  by (unfold Upper_def) simp
+
+theorem (in partial_order) complete_lattice_criterion1:
+  assumes top_exists: "EX g. greatest L g (carrier L)"
+    and inf_exists:
+      "!!A. [| A \<subseteq> carrier L; A ~= {} |] ==> EX i. greatest L i (Lower L A)"
+  shows "complete_lattice L"
+proof (rule complete_latticeI)
+  from top_exists obtain top where top: "greatest L top (carrier L)" ..
+  fix A
+  assume L: "A \<subseteq> carrier L"
+  let ?B = "Upper L A"
+  from L top have "top \<in> ?B" by (fast intro!: Upper_memI intro: greatest_le)
+  then have B_non_empty: "?B ~= {}" by fast
+  have B_L: "?B \<subseteq> carrier L" by simp
+  from inf_exists [OF B_L B_non_empty]
+  obtain b where b_inf_B: "greatest L b (Lower L ?B)" ..
+  have "least L b (Upper L A)"
+apply (rule least_UpperI)
+   apply (rule greatest_le [where A = "Lower L ?B"]) 
+    apply (rule b_inf_B)
+   apply (rule Lower_memI)
+    apply (erule UpperD)
+     apply assumption
+    apply (rule L)
+   apply (fast intro: L [THEN subsetD])
+  apply (erule greatest_Lower_above [OF b_inf_B])
+  apply simp
+ apply (rule L)
+apply (rule greatest_carrier [OF b_inf_B]) (* rename rule: _closed *)
+done
+  then show "EX s. least L s (Upper L A)" ..
+next
+  fix A
+  assume L: "A \<subseteq> carrier L"
+  show "EX i. greatest L i (Lower L A)"
+  proof (cases "A = {}")
+    case True then show ?thesis
+      by (simp add: top_exists)
+  next
+    case False with L show ?thesis
+      by (rule inf_exists)
+  qed
+qed
+
+(* TODO: prove dual version *)
+
+subsection {* Examples *}
+
+subsubsection {* Powerset of a set is a complete lattice *}
+
+theorem powerset_is_complete_lattice:
+  "complete_lattice (| carrier = Pow A, le = op \<subseteq> |)"
+  (is "complete_lattice ?L")
+proof (rule partial_order.complete_latticeI)
+  show "partial_order ?L"
+    by (rule partial_order.intro) auto
+next
+  fix B
+  assume "B \<subseteq> carrier ?L"
+  then have "least ?L (\<Union> B) (Upper ?L B)"
+    by (fastsimp intro!: least_UpperI simp: Upper_def)
+  then show "EX s. least ?L s (Upper ?L B)" ..
+next
+  fix B
+  assume "B \<subseteq> carrier ?L"
+  then have "greatest ?L (\<Inter> B \<inter> A) (Lower ?L B)"
+    txt {* @{term "\<Inter> B"} is not the infimum of @{term B}:
+      @{term "\<Inter> {} = UNIV"} which is in general bigger than @{term "A"}! *}
+    by (fastsimp intro!: greatest_LowerI simp: Lower_def)
+  then show "EX i. greatest ?L i (Lower ?L B)" ..
+qed
+
+subsubsection {* Lattice of subgroups of a group *}
+
+theorem (in group) subgroups_partial_order:
+  "partial_order (| carrier = {H. subgroup H G}, le = op \<subseteq> |)"
+  by (rule partial_order.intro) simp_all
+
+lemma (in group) subgroup_self:
+  "subgroup (carrier G) G"
+  by (rule subgroupI) auto
+
+lemma (in group) subgroup_imp_group:
+  "subgroup H G ==> group (G(| carrier := H |))"
+  using subgroup.groupI [OF _ group.intro] .
+
+lemma (in group) is_monoid [intro, simp]:
+  "monoid G"
+  by (rule monoid.intro)
+
+lemma (in group) subgroup_inv_equality:
+  "[| subgroup H G; x \<in> H |] ==> m_inv (G (| carrier := H |)) x = inv x"
+apply (rule_tac inv_equality [THEN sym])
+  apply (rule group.l_inv [OF subgroup_imp_group, simplified])
+   apply assumption+
+ apply (rule subsetD [OF subgroup.subset])
+  apply assumption+
+apply (rule subsetD [OF subgroup.subset])
+ apply assumption
+apply (rule_tac group.inv_closed [OF subgroup_imp_group, simplified])
+  apply assumption+
+done
+
+theorem (in group) subgroups_Inter:
+  assumes subgr: "(!!H. H \<in> A ==> subgroup H G)"
+    and not_empty: "A ~= {}"
+  shows "subgroup (\<Inter>A) G"
+proof (rule subgroupI)
+  from subgr [THEN subgroup.subset] and not_empty
+  show "\<Inter>A \<subseteq> carrier G" by blast
+next
+  from subgr [THEN subgroup.one_closed]
+  show "\<Inter>A ~= {}" by blast
+next
+  fix x assume "x \<in> \<Inter>A"
+  with subgr [THEN subgroup.m_inv_closed]
+  show "inv x \<in> \<Inter>A" by blast
+next
+  fix x y assume "x \<in> \<Inter>A" "y \<in> \<Inter>A"
+  with subgr [THEN subgroup.m_closed]
+  show "x \<otimes> y \<in> \<Inter>A" by blast
+qed
+
+theorem (in group) subgroups_complete_lattice:
+  "complete_lattice (| carrier = {H. subgroup H G}, le = op \<subseteq> |)"
+    (is "complete_lattice ?L")
+proof (rule partial_order.complete_lattice_criterion1)
+  show "partial_order ?L" by (rule subgroups_partial_order)
+next
+  have "greatest ?L (carrier G) (carrier ?L)"
+    by (unfold greatest_def) (simp add: subgroup.subset subgroup_self)
+  then show "EX G. greatest ?L G (carrier ?L)" ..
+next
+  fix A
+  assume L: "A \<subseteq> carrier ?L" and non_empty: "A ~= {}"
+  then have Int_subgroup: "subgroup (\<Inter>A) G"
+    by (fastsimp intro: subgroups_Inter)
+  have "greatest ?L (\<Inter>A) (Lower ?L A)"
+    (is "greatest ?L ?Int _")
+  proof (rule greatest_LowerI)
+    fix H
+    assume H: "H \<in> A"
+    with L have subgroupH: "subgroup H G" by auto
+    from subgroupH have submagmaH: "submagma H G" by (rule subgroup.axioms)
+    from subgroupH have groupH: "group (G (| carrier := H |))" (is "group ?H")
+      by (rule subgroup_imp_group)
+    from groupH have monoidH: "monoid ?H"
+      by (rule group.is_monoid)
+    from H have Int_subset: "?Int \<subseteq> H" by fastsimp
+    then show "le ?L ?Int H" by simp
+  next
+    fix H
+    assume H: "H \<in> Lower ?L A"
+    with L Int_subgroup show "le ?L H ?Int" by (fastsimp intro: Inter_greatest)
+  next
+    show "A \<subseteq> carrier ?L" by (rule L)
+  next
+    show "?Int \<in> carrier ?L" by simp (rule Int_subgroup)
+  qed
+  then show "EX I. greatest ?L I (Lower ?L A)" ..
+qed
+
+end
\ No newline at end of file
diff -r b13da5649bf9 -r 2cb6ff394bfb src/HOL/Algebra/ROOT.ML
--- a/src/HOL/Algebra/ROOT.ML	Tue Apr 13 07:48:32 2004 +0200
+++ b/src/HOL/Algebra/ROOT.ML	Tue Apr 13 09:42:40 2004 +0200
@@ -16,6 +16,7 @@
 use_thy "FiniteProduct";	(* Product operator for commutative groups *)
 use_thy "Sylow";		(* Sylow's theorem *)
 use_thy "Bij";			(* Automorphism Groups *)
+use_thy "Lattice";              (* Lattices, and the complete lattice of subgroups *)
 
 (* Rings *)
 
diff -r b13da5649bf9 -r 2cb6ff394bfb src/HOL/Algebra/document/root.tex
--- a/src/HOL/Algebra/document/root.tex	Tue Apr 13 07:48:32 2004 +0200
+++ b/src/HOL/Algebra/document/root.tex	Tue Apr 13 09:42:40 2004 +0200
@@ -22,7 +22,7 @@
                                        %   \<twosuperior>, \<onehalf>,
                                        %   \<threesuperior>, \<threequarters>
                                        %   \<degree>
-%\usepackage[only,bigsqcap]{stmaryrd}  % for \<Sqinter>
+\usepackage[only,bigsqcap]{stmaryrd}  % for \<Sqinter>
 %\usepackage{wasysym}
 %\usepackage{eufrak}                   % for \<AA> ... \<ZZ>, \<aa> ... \<zz>
 %\usepackage{textcomp}                  % for \<zero> ... \<nine>, \<cent>
diff -r b13da5649bf9 -r 2cb6ff394bfb src/HOL/IsaMakefile
--- a/src/HOL/IsaMakefile	Tue Apr 13 07:48:32 2004 +0200
+++ b/src/HOL/IsaMakefile	Tue Apr 13 09:42:40 2004 +0200
@@ -341,6 +341,7 @@
   Algebra/Exponent.thy \
   Algebra/FiniteProduct.thy \
   Algebra/Group.thy \
+  Algebra/Lattice.thy \
   Algebra/Module.thy \
   Algebra/Sylow.thy \
   Algebra/UnivPoly.thy \
diff -r b13da5649bf9 -r 2cb6ff394bfb src/HOL/Set.thy
--- a/src/HOL/Set.thy	Tue Apr 13 07:48:32 2004 +0200
+++ b/src/HOL/Set.thy	Tue Apr 13 09:42:40 2004 +0200
@@ -943,6 +943,10 @@
 lemma Inter_lower: "B \<in> A ==> Inter A \<subseteq> B"
   by blast
 
+lemma Inter_subset:
+  "[| !!X. X \<in> A ==> X \<subseteq> B; A ~= {} |] ==> \<Inter>A \<subseteq> B"
+  by blast
+
 lemma Inter_greatest: "(!!X. X \<in> A ==> C \<subseteq> X) ==> C \<subseteq> Inter A"
   by (rules intro: InterI subsetI dest: subsetD)