Theory IFOL

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theory IFOL
imports Pure
uses (IFOL_lemmas.ML) (fologic.ML) (hypsubstdata.ML) (intprover.ML) [IFOL.ML]
begin

(*  Title:      FOL/IFOL.thy
    ID:         $Id: IFOL.thy,v 1.49 2005/09/28 22:58:55 wenzelm Exp $
    Author:     Lawrence C Paulson and Markus Wenzel
*)

header {* Intuitionistic first-order logic *}

theory IFOL
imports Pure
uses ("IFOL_lemmas.ML") ("fologic.ML") ("hypsubstdata.ML") ("intprover.ML")
begin


subsection {* Syntax and axiomatic basis *}

global

classes "term"
final_consts term_class
defaultsort "term"

typedecl o

judgment
  Trueprop      :: "o => prop"                  ("(_)" 5)

consts
  True          :: o
  False         :: o

  (* Connectives *)

  "op ="        :: "['a, 'a] => o"              (infixl "=" 50)

  Not           :: "o => o"                     ("~ _" [40] 40)
  "op &"        :: "[o, o] => o"                (infixr "&" 35)
  "op |"        :: "[o, o] => o"                (infixr "|" 30)
  "op -->"      :: "[o, o] => o"                (infixr "-->" 25)
  "op <->"      :: "[o, o] => o"                (infixr "<->" 25)

  (* Quantifiers *)

  All           :: "('a => o) => o"             (binder "ALL " 10)
  Ex            :: "('a => o) => o"             (binder "EX " 10)
  Ex1           :: "('a => o) => o"             (binder "EX! " 10)


syntax
  "_not_equal"  :: "['a, 'a] => o"              (infixl "~=" 50)
translations
  "x ~= y"      == "~ (x = y)"

syntax (xsymbols)
  Not           :: "o => o"                     ("¬ _" [40] 40)
  "op &"        :: "[o, o] => o"                (infixr "∧" 35)
  "op |"        :: "[o, o] => o"                (infixr "∨" 30)
  "ALL "        :: "[idts, o] => o"             ("(3∀_./ _)" [0, 10] 10)
  "EX "         :: "[idts, o] => o"             ("(3∃_./ _)" [0, 10] 10)
  "EX! "        :: "[idts, o] => o"             ("(3∃!_./ _)" [0, 10] 10)
  "_not_equal"  :: "['a, 'a] => o"              (infixl "≠" 50)
  "op -->"      :: "[o, o] => o"                (infixr "-->" 25)
  "op <->"      :: "[o, o] => o"                (infixr "<->" 25)

syntax (HTML output)
  Not           :: "o => o"                     ("¬ _" [40] 40)
  "op &"        :: "[o, o] => o"                (infixr "∧" 35)
  "op |"        :: "[o, o] => o"                (infixr "∨" 30)
  "ALL "        :: "[idts, o] => o"             ("(3∀_./ _)" [0, 10] 10)
  "EX "         :: "[idts, o] => o"             ("(3∃_./ _)" [0, 10] 10)
  "EX! "        :: "[idts, o] => o"             ("(3∃!_./ _)" [0, 10] 10)
  "_not_equal"  :: "['a, 'a] => o"              (infixl "≠" 50)


local

finalconsts
  False All Ex
  "op ="
  "op &"
  "op |"
  "op -->"

axioms

  (* Equality *)

  refl:         "a=a"

  (* Propositional logic *)

  conjI:        "[| P;  Q |] ==> P&Q"
  conjunct1:    "P&Q ==> P"
  conjunct2:    "P&Q ==> Q"

  disjI1:       "P ==> P|Q"
  disjI2:       "Q ==> P|Q"
  disjE:        "[| P|Q;  P ==> R;  Q ==> R |] ==> R"

  impI:         "(P ==> Q) ==> P-->Q"
  mp:           "[| P-->Q;  P |] ==> Q"

  FalseE:       "False ==> P"

  (* Quantifiers *)

  allI:         "(!!x. P(x)) ==> (ALL x. P(x))"
  spec:         "(ALL x. P(x)) ==> P(x)"

  exI:          "P(x) ==> (EX x. P(x))"
  exE:          "[| EX x. P(x);  !!x. P(x) ==> R |] ==> R"

  (* Reflection *)

  eq_reflection:  "(x=y)   ==> (x==y)"
  iff_reflection: "(P<->Q) ==> (P==Q)"


text{*Thanks to Stephan Merz*}
theorem subst:
  assumes eq: "a = b" and p: "P(a)"
  shows "P(b)"
proof -
  from eq have meta: "a ≡ b"
    by (rule eq_reflection)
  from p show ?thesis
    by (unfold meta)
qed


defs
  (* Definitions *)

  True_def:     "True  == False-->False"
  not_def:      "~P    == P-->False"
  iff_def:      "P<->Q == (P-->Q) & (Q-->P)"

  (* Unique existence *)

  ex1_def:      "Ex1(P) == EX x. P(x) & (ALL y. P(y) --> y=x)"


subsection {* Lemmas and proof tools *}

use "IFOL_lemmas.ML"

use "fologic.ML"
use "hypsubstdata.ML"
setup hypsubst_setup
use "intprover.ML"


subsection {* Intuitionistic Reasoning *}

lemma impE':
  assumes 1: "P --> Q"
    and 2: "Q ==> R"
    and 3: "P --> Q ==> P"
  shows R
proof -
  from 3 and 1 have P .
  with 1 have Q by (rule impE)
  with 2 show R .
qed

lemma allE':
  assumes 1: "ALL x. P(x)"
    and 2: "P(x) ==> ALL x. P(x) ==> Q"
  shows Q
proof -
  from 1 have "P(x)" by (rule spec)
  from this and 1 show Q by (rule 2)
qed

lemma notE':
  assumes 1: "~ P"
    and 2: "~ P ==> P"
  shows R
proof -
  from 2 and 1 have P .
  with 1 show R by (rule notE)
qed

lemmas [Pure.elim!] = disjE iffE FalseE conjE exE
  and [Pure.intro!] = iffI conjI impI TrueI notI allI refl
  and [Pure.elim 2] = allE notE' impE'
  and [Pure.intro] = exI disjI2 disjI1

setup {*
  [ContextRules.addSWrapper (fn tac => hyp_subst_tac ORELSE' tac)]
*}


lemma iff_not_sym: "~ (Q <-> P) ==> ~ (P <-> Q)"
  by iprover

lemmas [sym] = sym iff_sym not_sym iff_not_sym
  and [Pure.elim?] = iffD1 iffD2 impE


lemma eq_commute: "a=b <-> b=a"
apply (rule iffI) 
apply (erule sym)+
done


subsection {* Atomizing meta-level rules *}

lemma atomize_all [atomize]: "(!!x. P(x)) == Trueprop (ALL x. P(x))"
proof
  assume "!!x. P(x)"
  show "ALL x. P(x)" ..
next
  assume "ALL x. P(x)"
  thus "!!x. P(x)" ..
qed

lemma atomize_imp [atomize]: "(A ==> B) == Trueprop (A --> B)"
proof
  assume "A ==> B"
  thus "A --> B" ..
next
  assume "A --> B" and A
  thus B by (rule mp)
qed

lemma atomize_eq [atomize]: "(x == y) == Trueprop (x = y)"
proof
  assume "x == y"
  show "x = y" by (unfold prems) (rule refl)
next
  assume "x = y"
  thus "x == y" by (rule eq_reflection)
qed

lemma atomize_conj [atomize]:
  "(!!C. (A ==> B ==> PROP C) ==> PROP C) == Trueprop (A & B)"
proof
  assume "!!C. (A ==> B ==> PROP C) ==> PROP C"
  show "A & B" by (rule conjI)
next
  fix C
  assume "A & B"
  assume "A ==> B ==> PROP C"
  thus "PROP C"
  proof this
    show A by (rule conjunct1)
    show B by (rule conjunct2)
  qed
qed

lemmas [symmetric, rulify] = atomize_all atomize_imp


subsection {* Calculational rules *}

lemma forw_subst: "a = b ==> P(b) ==> P(a)"
  by (rule ssubst)

lemma back_subst: "P(a) ==> a = b ==> P(b)"
  by (rule subst)

text {*
  Note that this list of rules is in reverse order of priorities.
*}

lemmas basic_trans_rules [trans] =
  forw_subst
  back_subst
  rev_mp
  mp
  trans

subsection {* ``Let'' declarations *}

nonterminals letbinds letbind

constdefs
  Let :: "['a::{}, 'a => 'b] => ('b::{})"
    "Let(s, f) == f(s)"

syntax
  "_bind"       :: "[pttrn, 'a] => letbind"           ("(2_ =/ _)" 10)
  ""            :: "letbind => letbinds"              ("_")
  "_binds"      :: "[letbind, letbinds] => letbinds"  ("_;/ _")
  "_Let"        :: "[letbinds, 'a] => 'a"             ("(let (_)/ in (_))" 10)

translations
  "_Let(_binds(b, bs), e)"  == "_Let(b, _Let(bs, e))"
  "let x = a in e"          == "Let(a, %x. e)"


lemma LetI: 
    assumes prem: "(!!x. x=t ==> P(u(x)))"
    shows "P(let x=t in u(x))"
apply (unfold Let_def)
apply (rule refl [THEN prem])
done

ML
{*
val Let_def = thm "Let_def";
val LetI = thm "LetI";
*}

end

Syntax and axiomatic basis

theorem subst:

  [| a = b; P(a) |] ==> P(b)

Lemmas and proof tools

theorem TrueI:

  True

theorem conjE:

  [| PQ; [| P; Q |] ==> R |] ==> R

theorem impE:

  [| P --> Q; P; Q ==> R |] ==> R

theorem allE:

  [| ∀x. P(x); P(x) ==> R |] ==> R

theorem all_dupE:

  [| ∀x. P(x); [| P(x); ∀x. P(x) |] ==> R |] ==> R

theorem notI:

  (P ==> False) ==> ¬ P

theorem notE:

  [| ¬ P; P |] ==> R

theorem rev_notE:

  [| P; ¬ P |] ==> R

theorem not_to_imp:

  [| ¬ P; P --> False ==> Q |] ==> Q

theorem rev_mp:

  [| P; P --> Q |] ==> Q

theorem contrapos:

  [| ¬ Q; P ==> Q |] ==> ¬ P

theorem iffI:

  [| P ==> Q; Q ==> P |] ==> P <-> Q

theorem iffE:

  [| P <-> Q; [| P --> Q; Q --> P |] ==> R |] ==> R

theorem iffD1:

  [| P <-> Q; P |] ==> Q

theorem iffD2:

  [| P <-> Q; Q |] ==> P

theorem rev_iffD1:

  [| P; P <-> Q |] ==> Q

theorem rev_iffD2:

  [| Q; P <-> Q |] ==> P

theorem iff_refl:

  P <-> P

theorem iff_sym:

  Q <-> P ==> P <-> Q

theorem iff_trans:

  [| P <-> Q; Q <-> R |] ==> P <-> R

theorem ex1I:

  [| P(a); !!x. P(x) ==> x = a |] ==> ∃!x. P(x)

theorem ex_ex1I:

  [| ∃x. P(x); !!x y. [| P(x); P(y) |] ==> x = y |] ==> ∃!x. P(x)

theorem ex1E:

  [| ∃!x. P(x); !!x. [| P(x); ∀y. P(y) --> y = x |] ==> R |] ==> R

theorem conj_cong:

  [| P <-> P'; P' ==> Q <-> Q' |] ==> PQ <-> P'Q'

theorem conj_cong2:

  [| P <-> P'; P' ==> Q <-> Q' |] ==> QP <-> Q'P'

theorem disj_cong:

  [| P <-> P'; Q <-> Q' |] ==> PQ <-> P'Q'

theorem imp_cong:

  [| P <-> P'; P' ==> Q <-> Q' |] ==> (P --> Q) <-> P' --> Q'

theorem iff_cong:

  [| P <-> P'; Q <-> Q' |] ==> (P <-> Q) <-> P' <-> Q'

theorem not_cong:

  P <-> P' ==> ¬ P <-> ¬ P'

theorem all_cong:

  (!!x. P(x) <-> Q(x)) ==> (∀x. P(x)) <-> (∀x. Q(x))

theorem ex_cong:

  (!!x. P(x) <-> Q(x)) ==> (∃x. P(x)) <-> (∃x. Q(x))

theorem ex1_cong:

  (!!x. P(x) <-> Q(x)) ==> (∃!x. P(x)) <-> (∃!x. Q(x))

theorem sym:

  a = b ==> b = a

theorem trans:

  [| a = b; b = c |] ==> a = c

theorem not_sym:

  ba ==> ab

theorem def_imp_iff:

  A == B ==> A <-> B

theorem meta_eq_to_obj_eq:

  A == B ==> A = B

theorem ssubst:

  [| b = a; P(a) |] ==> P(b)

theorem ex1_equalsE:

  [| ∃!x. P(x); P(a); P(b) |] ==> a = b

theorem subst_context:

  a = b ==> t(a) = t(b)

theorem subst_context2:

  [| a = b; c = d |] ==> t(a, c) = t(b, d)

theorem subst_context3:

  [| a = b; c = d; e = f |] ==> t(a, c, e) = t(b, d, f)

theorem box_equals:

  [| a = b; a = c; b = d |] ==> c = d

theorem simp_equals:

  [| a = c; b = d; c = d |] ==> a = b

theorem pred1_cong:

  a = a' ==> P(a) <-> P(a')

theorem pred2_cong:

  [| a = a'; b = b' |] ==> P(a, b) <-> P(a', b')

theorem pred3_cong:

  [| a = a'; b = b'; c = c' |] ==> P(a, b, c) <-> P(a', b', c')

theorem eq_cong:

  [| a = a'; b = b' |] ==> a = b <-> a' = b'

theorem conj_impE:

  [| PQ --> S; P --> Q --> S ==> R |] ==> R

theorem disj_impE:

  [| PQ --> S; [| P --> S; Q --> S |] ==> R |] ==> R

theorem imp_impE:

  [| (P --> Q) --> S; [| P; Q --> S |] ==> Q; S ==> R |] ==> R

theorem not_impE:

  [| ¬ P --> S; P ==> False; S ==> R |] ==> R

theorem iff_impE:

  [| (P <-> Q) --> S; [| P; Q --> S |] ==> Q; [| Q; P --> S |] ==> P; S ==> R |]
  ==> R

theorem all_impE:

  [| (∀x. P(x)) --> S; !!x. P(x); S ==> R |] ==> R

theorem ex_impE:

  [| (∃x. P(x)) --> S; P(x) --> S ==> R |] ==> R

theorem disj_imp_disj:

  [| PQ; P ==> R; Q ==> S |] ==> RS

Intuitionistic Reasoning

lemma impE':

  [| P --> Q; Q ==> R; P --> Q ==> P |] ==> R

lemma allE':

  [| ∀x. P(x); [| P(x); ∀x. P(x) |] ==> Q |] ==> Q

lemma notE':

  [| ¬ P; ¬ P ==> P |] ==> R

lemmas

  [| PQ; P ==> R; Q ==> R |] ==> R
  [| P <-> Q; [| P --> Q; Q --> P |] ==> R |] ==> R
  False ==> P
  [| PQ; [| P; Q |] ==> R |] ==> R
  [| ∃x. P(x); !!x. P(x) ==> R |] ==> R

and

  [| P ==> Q; Q ==> P |] ==> P <-> Q
  [| P; Q |] ==> PQ
  (P ==> Q) ==> P --> Q
  True
  (P ==> False) ==> ¬ P
  (!!x. P(x)) ==> ∀x. P(x)
  a = a

and

  [| ∀x. P(x); P(x) ==> R |] ==> R
  [| ¬ P; ¬ P ==> P |] ==> R
  [| P --> Q; Q ==> R; P --> Q ==> P |] ==> R

and

  P(x) ==> ∃x. P(x)
  Q ==> PQ
  P ==> PQ

lemmas

  [| PQ; P ==> R; Q ==> R |] ==> R
  [| P <-> Q; [| P --> Q; Q --> P |] ==> R |] ==> R
  False ==> P
  [| PQ; [| P; Q |] ==> R |] ==> R
  [| ∃x. P(x); !!x. P(x) ==> R |] ==> R

and

  [| P ==> Q; Q ==> P |] ==> P <-> Q
  [| P; Q |] ==> PQ
  (P ==> Q) ==> P --> Q
  True
  (P ==> False) ==> ¬ P
  (!!x. P(x)) ==> ∀x. P(x)
  a = a

and

  [| ∀x. P(x); P(x) ==> R |] ==> R
  [| ¬ P; ¬ P ==> P |] ==> R
  [| P --> Q; Q ==> R; P --> Q ==> P |] ==> R

and

  P(x) ==> ∃x. P(x)
  Q ==> PQ
  P ==> PQ

lemma iff_not_sym:

  ¬ (Q <-> P) ==> ¬ (P <-> Q)

lemmas

  a = b ==> b = a
  Q <-> P ==> P <-> Q
  ba ==> ab
  ¬ (Q <-> P) ==> ¬ (P <-> Q)

and

  [| P <-> Q; P |] ==> Q
  [| P <-> Q; Q |] ==> P
  [| P --> Q; P; Q ==> R |] ==> R

lemmas

  a = b ==> b = a
  Q <-> P ==> P <-> Q
  ba ==> ab
  ¬ (Q <-> P) ==> ¬ (P <-> Q)

and

  [| P <-> Q; P |] ==> Q
  [| P <-> Q; Q |] ==> P
  [| P --> Q; P; Q ==> R |] ==> R

lemma eq_commute:

  a = b <-> b = a

Atomizing meta-level rules

lemma atomize_all:

  (!!x. P(x)) == ∀x. P(x)

lemma atomize_imp:

  (A ==> B) == A --> B

lemma atomize_eq:

  (x == y) == x = y

lemma atomize_conj:

  (A && B) == AB

lemmas

x. P1(x) == (!!x. P1(x))
  A1 --> B1 == (A1 ==> B1)

lemmas

x. P1(x) == (!!x. P1(x))
  A1 --> B1 == (A1 ==> B1)

Calculational rules

lemma forw_subst:

  [| a = b; P(b) |] ==> P(a)

lemma back_subst:

  [| P(a); a = b |] ==> P(b)

lemmas basic_trans_rules:

  [| a = b; P(b) |] ==> P(a)
  [| P(a); a = b |] ==> P(b)
  [| P; P --> Q |] ==> Q
  [| P --> Q; P |] ==> Q
  [| a = b; b = c |] ==> a = c

lemmas basic_trans_rules:

  [| a = b; P(b) |] ==> P(a)
  [| P(a); a = b |] ==> P(b)
  [| P; P --> Q |] ==> Q
  [| P --> Q; P |] ==> Q
  [| a = b; b = c |] ==> a = c

``Let'' declarations

lemma LetI:

  (!!x. x = t ==> P(u(x))) ==> P(Let(t, u))