(* Title: ZF/Tools/inductive_package.ML Author: Lawrence C Paulson, Cambridge University Computer Laboratory
Fixedpoint definition module -- for Inductive/Coinductive Definitions
The functor will be instantiated for normal sums/products (inductive defs) and non-standard sums/products (coinductive defs)
Sums are used only for mutual recursion; Products are used only to derive "streamlined" induction rules for relations
*)
type inductive_result =
{defs : thm list, (*definitions made in thy*)
bnd_mono : thm, (*monotonicity for the lfp definition*)
dom_subset : thm, (*inclusion of recursive set in dom*)
intrs : thm list, (*introduction rules*)
elim : thm, (*case analysis theorem*)
induct : thm, (*main induction rule*)
mutual_induct : thm}; (*mutual induction rule*)
(*Functor's result signature*) signature INDUCTIVE_PACKAGE = sig (*Insert definitions for the recursive sets, which
must *already* be declared as constants in parent theory!*) val add_inductive_i: bool -> term list * term ->
((binding * term) * attribute list) list ->
thm list * thm list * thm list * thm list -> theory -> theory * inductive_result val add_inductive: stringlist * string ->
((binding * string) * Token.src list) list ->
(Facts.ref * Token.src list) list * (Facts.ref * Token.src list) list *
(Facts.ref * Token.src list) list * (Facts.ref * Token.src list) list ->
theory -> theory * inductive_result end;
(*Declares functions to add fixedpoint/constructor defs to a theory.
Recursive sets must *already* be declared as constants.*)
functor Add_inductive_def_Fun
(structure Fp: FP and Pr : PR and CP: CARTPROD and Su : SU val coind: bool)
: INDUCTIVE_PACKAGE = struct
val co_prefix = if coind then"co"else"";
(* utils *)
(*make distinct individual variables a1, a2, a3, ..., an. *) fun mk_frees a [] = []
| mk_frees a (T::Ts) = Free(a,T) :: mk_frees (Symbol.bump_string a) Ts;
(* add_inductive(_i) *)
(*internal version, accepting terms*) fun add_inductive_i verbose (rec_tms, dom_sum)
raw_intr_specs (monos, con_defs, type_intrs, type_elims) thy0 = let val ctxt0 = Proof_Context.init_global thy0;
val intr_specs = map (apfst (apfst Binding.name_of)) raw_intr_specs; val (intr_names, intr_tms) = split_list (map fst intr_specs); val case_names = Rule_Cases.case_names intr_names;
(*recT and rec_params should agree for all mutually recursive components*) val rec_hds = map head_of rec_tms;
val dummy = rec_hds |> forall (fn t => is_Const t orelse
error ("Recursive set not previously declared as constant: " ^
Syntax.string_of_term ctxt0 t));
(*Now we know they are all Consts, so get their names, type and params*) val rec_names = map dest_Const_name rec_hds and (Const(_,recT),rec_params) = strip_comb (hd rec_tms);
val rec_base_names = map Long_Name.base_name rec_names; val dummy = rec_base_names |> forall (fn a => Symbol_Pos.is_identifier a orelse
error ("Base name of recursive set not an identifier: " ^ a));
local (*Checking the introduction rules*) val intr_sets = map (#2 o Ind_Syntax.rule_concl_msg thy0) intr_tms; fun intr_ok set = case head_of setofConst(a,recT) => member (op =) rec_names a | _ => false; in val dummy = intr_sets |> forall (fn t => intr_ok t orelse
error ("Conclusion of rule does not name a recursive set: " ^
Syntax.string_of_term ctxt0 t)); end;
val dummy = rec_params |> forall (fn t => is_Free t orelse
error ("Param in recursion term not a free variable: " ^
Syntax.string_of_term ctxt0 t));
(*** Construct the fixedpoint definition ***) val mk_variant = singleton (Name.variant_list (List.foldr Misc_Legacy.add_term_names [] intr_tms));
val z' = mk_variant"z" and X' = mk_variant"X"and w' = mk_variant"w";
fun dest_tprop \<^Const_>\<open>Trueprop for P\<close> = P
| dest_tprop Q = error ("Ill-formed premise of introduction rule: " ^
Syntax.string_of_term ctxt0 Q);
(*Makes a disjunct from an introduction rule*) fun fp_part intr = (*quantify over rule's free vars except parameters*) letval prems = map dest_tprop (Logic.strip_imp_prems intr) val dummy = List.app (fn rec_hd => List.app (Ind_Syntax.chk_prem rec_hd) prems) rec_hds val exfrees = subtract (op =) rec_params (Misc_Legacy.term_frees intr) val zeq = FOLogic.mk_eq (Free(z', \<^Type>\i\), #1 (Ind_Syntax.rule_concl intr)) in
fold_rev (FOLogic.mk_exists o Term.dest_Free) exfrees
(Balanced_Tree.make FOLogic.mk_conj (zeq::prems)) end;
(*The Part(A,h) terms -- compose injections to make h*) fun mk_Part (Bound 0) = Free(X', \<^Type>\i\) (*no mutual rec, no Part needed*)
| mk_Part h = \<^Const>\<open>Part\<close> $ Free(X', \<^Type>\i\) $ Abs (w', \<^Type>\<open>i\<close>, h);
(*Access to balanced disjoint sums via injections*) val parts = map mk_Part
(Balanced_Tree.accesses {left = fn t => Su.inl $ t, right = fn t => Su.inr $ t, init = Bound 0}
(length rec_tms));
(*replace each set by the corresponding Part(A,h)*) val part_intrs = map (subst_free (rec_tms ~~ parts) o fp_part) intr_tms;
val dummy = List.app (fn rec_hd => (Logic.occs (rec_hd, fp_rhs) andalso
error "Illegal occurrence of recursion operator"; ()))
rec_hds;
(*** Make the new theory ***)
(*A key definition: If no mutual recursion then it equals the one recursive set.
If mutual recursion then it differs from all the recursive sets. *) val big_rec_base_name = space_implode "_" rec_base_names; val big_rec_name = Proof_Context.intern_const ctxt0 big_rec_base_name;
val _ = if verbose then
writeln ((if coind then"Coind"else"Ind") ^ "uctive definition " ^ quote big_rec_name) else ();
(*Big_rec... is the union of the mutually recursive sets*) val big_rec_tm = list_comb(Const(big_rec_name,recT), rec_params);
(*The individual sets must already be declared*) val axpairs = map Misc_Legacy.mk_defpair
((big_rec_tm, fp_rhs) ::
(case parts of
[_] => [] (*no mutual recursion*)
| _ => rec_tms ~~ (*define the sets as Parts*) map (subst_atomic [(Free (X', \<^Type>\i\), big_rec_tm)]) parts));
(*tracing: print the fixedpoint definition*) val dummy = if !Ind_Syntax.trace then
writeln (cat_lines (map (Syntax.string_of_term ctxt0 o #2) axpairs)) else ()
(*add definitions of the inductive sets*) val thy1 =
thy0
|> Sign.add_path big_rec_base_name
|> fold (snd oo Global_Theory.add_def o apfst Binding.name) axpairs;
(*fetch fp definitions from the theory*) val big_rec_def::part_rec_defs = map (Misc_Legacy.get_def thy1)
(case rec_names of [_] => rec_names
| _ => big_rec_base_name::rec_names);
(********) val dummy = writeln " Proving monotonicity...";
val unfold = Drule.export_without_context ([big_rec_def, bnd_mono] MRS Fp.Tarski);
(********) val dummy = writeln " Proving the introduction rules...";
(*Mutual recursion? Helps to derive subset rules for the
individual sets.*) val Part_trans = case rec_names of
[_] => asm_rl
| _ => Drule.export_without_context (@{thm Part_subset} RS @{thm subset_trans});
(*To type-check recursive occurrences of the inductive sets, possibly
enclosed in some monotonic operator M.*) val rec_typechecks =
[dom_subset] RL (asm_rl :: ([Part_trans] RL monos))
RL [@{thm subsetD}];
(*Type-checking is hardest aspect of proof;
disjIn selects the correct disjunct after unfolding*) fun intro_tacsf disjIn ctxt =
[DETERM (stac ctxt unfold 1),
REPEAT (resolve_tac ctxt [@{thm Part_eqI}, @{thm CollectI}] 1), (*Now 2-3 subgoals: typechecking, the disjunction, perhaps equality.*)
resolve_tac ctxt [disjIn] 2, (*Not ares_tac, since refl must be tried before equality assumptions;
backtracking may occur if the premises have extra variables!*)
DEPTH_SOLVE_1 (resolve_tac ctxt [@{thm refl}, @{thm exI}, @{thm conjI}] 2 APPEND assume_tac ctxt 2), (*Now solve the equations like Tcons(a,f) = Inl(?b4)*)
rewrite_goals_tac ctxt con_defs,
REPEAT (resolve_tac ctxt @{thms refl} 2), (*Typechecking; this can fail*) if !Ind_Syntax.trace then print_tac ctxt "The type-checking subgoal:" else all_tac,
REPEAT (FIRSTGOAL (dresolve_tac ctxt rec_typechecks
ORELSE' eresolve_tac ctxt (asm_rl :: @{thm PartE} :: @{thm SigmaE2} ::
type_elims)
ORELSE' hyp_subst_tac ctxt)), if !Ind_Syntax.trace then print_tac ctxt "The subgoal after monos, type_elims:" else all_tac,
DEPTH_SOLVE (swap_res_tac ctxt (@{thm SigmaI} :: @{thm subsetI} :: type_intrs) 1)];
(*combines disjI1 and disjI2 to get the corresponding nested disjunct...*) val mk_disj_rls = Balanced_Tree.accesses
{left = fn rl => rl RS @{thm disjI1},
right = fn rl => rl RS @{thm disjI2},
init = @{thm asm_rl}};
(*Applies freeness of the given constructors, which *must* be unfolded by the given defs. Cannot simply use the local con_defs because con_defs=[] for inference systems.
Proposition A should have the form t:Si where Si is an inductive set*) fun make_cases ctxt A =
rule_by_tactic ctxt
(basic_elim_tac ctxt THEN ALLGOALS (asm_full_simp_tac ctxt) THEN basic_elim_tac ctxt)
(Thm.assume A RS Thm.transfer' ctxt elim')
|> Drule.export_without_context_open;
fun induction_rules raw_induct = let val dummy = writeln " Proving the induction rule...";
(*** Prove the main induction rule ***)
val pred_name = "P"; (*name for predicate variables*)
(*Used to make induction rules; ind_alist = [(rec_tm1,pred1),...] associates predicates with rec ops
prem is a premise of an intr rule*) fun add_induct_prem ind_alist (prem as \<^Const_>\<open>Trueprop for \<^Const_>\<open>mem for t X\<close>\<close>, iprems) =
(case AList.lookup (op aconv) ind_alist X of
SOME pred => prem :: \<^make_judgment> (pred $ t) :: iprems
| NONE => (*possibly membership in M(rec_tm), for M monotone*) letfun mk_sb (rec_tm,pred) =
(rec_tm, \<^Const>\<open>Collect\<close> $ rec_tm $ pred) in subst_free (map mk_sb ind_alist) prem :: iprems end)
| add_induct_prem ind_alist (prem,iprems) = prem :: iprems;
(*Make a premise of the induction rule.*) fun induct_prem ind_alist intr = letval xs = subtract (op =) rec_params (Misc_Legacy.term_frees intr) val iprems = List.foldr (add_induct_prem ind_alist) []
(Logic.strip_imp_prems intr) val (t,X) = Ind_Syntax.rule_concl intr val (SOME pred) = AList.lookup (op aconv) ind_alist X val concl = \<^make_judgment> (pred $ t) in fold_rev Logic.all xs (Logic.list_implies (iprems,concl)) end handle Bind => error"Recursion term not found in conclusion";
(*Minimizes backtracking by delivering the correct premise to each goal.
Intro rules with extra Vars in premises still cause some backtracking *) fun ind_tac _ [] 0 = all_tac
| ind_tac ctxt (prem::prems) i =
DEPTH_SOLVE_1 (ares_tac ctxt [prem, @{thm refl}] i) THEN ind_tac ctxt prems (i-1);
val pred = Free(pred_name, \<^Type>\<open>i\<close> --> \<^Type>\<open>o\<close>);
val ind_prems = map (induct_prem (map (rpair pred) rec_tms))
intr_tms;
val dummy = if ! Ind_Syntax.trace then
writeln (cat_lines
(["ind_prems:"] @ map (Syntax.string_of_term ctxt4) ind_prems @
["raw_induct:", Thm.string_of_thm ctxt4 raw_induct])) else ();
(*We use a MINIMAL simpset. Even FOL_ss contains too many simpules.
If the premises get simplified, then the proofs could fail.*) val min_ss =
empty_simpset ctxt4
|> Simplifier.set_mksimps (fn ctxt => map mk_eq o ZF_atomize o Variable.gen_all ctxt)
|> Simplifier.set_unsafe_solver (mk_solver "minimal"
(fn ctxt => resolve_tac ctxt (triv_rls @ Simplifier.prems_of ctxt)
ORELSE' assume_tac ctxt
ORELSE' eresolve_tac ctxt @{thms FalseE}));
val quant_induct =
Goal.prove_global thy4 [] ind_prems
(\<^make_judgment> (Ind_Syntax.mk_all_imp (big_rec_tm, pred)))
(fn {context = ctxt, prems} => EVERY
[rewrite_goals_tac ctxt part_rec_defs,
resolve_tac ctxt [@{thm impI} RS @{thm allI}] 1,
DETERM (eresolve_tac ctxt [raw_induct] 1), (*Push Part inside Collect*)
full_simp_tac (min_ss |> Simplifier.add_simp @{thm Part_Collect}) 1, (*This CollectE and disjE separates out the introduction rules*)
REPEAT (FIRSTGOAL (eresolve_tac ctxt [@{thm CollectE}, @{thm disjE}])), (*Now break down the individual cases. No disjE here in case
some premise involves disjunction.*)
REPEAT (FIRSTGOAL (eresolve_tac ctxt [@{thm CollectE}, @{thm exE}, @{thm conjE}]
ORELSE' (bound_hyp_subst_tac ctxt))),
ind_tac ctxt (rev (map (rewrite_rule ctxt part_rec_defs) prems)) (length prems)]);
val dummy = if ! Ind_Syntax.trace then
writeln ("quant_induct:\n" ^ Thm.string_of_thm ctxt4 quant_induct) else ();
(*** Prove the simultaneous induction rule ***)
(*Make distinct predicates for each inductive set*)
(*The components of the element type, several if it is a product*) val elem_type = CP.pseudo_type dom_sum; val elem_factors = CP.factors elem_type; val elem_frees = mk_frees "za" elem_factors; val elem_tuple = CP.mk_tuple Pr.pair elem_type elem_frees;
(*Given a recursive set and its domain, return the "fsplit" predicate and a conclusion for the simultaneous induction rule. NOTE. This will not work for mutually recursive predicates. Previously a summand 'domt' was also an argument, but this required the domain of
mutual recursion to invariably be a disjoint sum.*) fun mk_predpair rec_tm = letval rec_name = dest_Const_name (head_of rec_tm) val pfree = Free(pred_name ^ "_" ^ Long_Name.base_name rec_name,
elem_factors ---> \<^Type>\<open>o\<close>) val qconcl =
fold_rev (FOLogic.mk_all o Term.dest_Free) elem_frees
\<^Const>\<open>imp for \<^Const>\<open>mem for elem_tuple rec_tm\<close> \<open>list_comb (pfree, elem_frees)\<close>\<close> in (CP.ap_split elem_type \<^Type>\<open>o\<close> pfree,
qconcl) end;
val (preds,qconcls) = split_list (map mk_predpair rec_tms);
(*Used to form simultaneous induction lemma*) fun mk_rec_imp (rec_tm,pred) =
\<^Const>\<open>imp for \<^Const>\<open>mem for \<open>Bound 0\<close> rec_tm\<close> \<open>pred $ Bound 0\<close>\<close>;
(*To instantiate the main induction rule*) val induct_concl =
\<^make_judgment>
(Ind_Syntax.mk_all_imp
(big_rec_tm,
Abs("z", \<^Type>\<open>i\<close>,
Balanced_Tree.make FOLogic.mk_conj
(ListPair.map mk_rec_imp (rec_tms, preds))))) and mutual_induct_concl =
\<^make_judgment> (Balanced_Tree.make FOLogic.mk_conj qconcls);
val dummy = if !Ind_Syntax.trace then
(writeln ("induct_concl = " ^
Syntax.string_of_term ctxt4 induct_concl);
writeln ("mutual_induct_concl = " ^
Syntax.string_of_term ctxt4 mutual_induct_concl)) else ();
val lemma = (*makes the link between the two induction rules*) if need_mutual then
(writeln " Proving the mutual induction rule...";
Goal.prove_global thy4 [] []
(Logic.mk_implies (induct_concl, mutual_induct_concl))
(fn {context = ctxt, ...} => EVERY
[rewrite_goals_tac ctxt part_rec_defs,
REPEAT (rewrite_goals_tac ctxt [Pr.split_eq] THEN lemma_tac ctxt 1)])) else (writeln " [ No mutual induction rule needed ]"; @{thm TrueI});
val dummy = if ! Ind_Syntax.trace then
writeln ("lemma: " ^ Thm.string_of_thm ctxt4 lemma) else ();
(*Mutual induction follows by freeness of Inl/Inr.*)
(*Simplification largely reduces the mutual induction rule to the
standard rule*) val mut_ss =
min_ss |> Simplifier.add_simps [Su.distinct, Su.distinct', Su.inl_iff, Su.inr_iff];
val all_defs = con_defs @ part_rec_defs;
(*Removes Collects caused by M-operators in the intro rules. It is very hard to simplify list({v: tf. (v : t --> P_t(v)) & (v : f --> P_f(v))}) where t==Part(tf,Inl) and f==Part(tf,Inr) to list({v: tf. P_t(v)}). Instead the following rules extract the relevant conjunct.
*) val cmonos = [@{thm subset_refl} RS @{thm Collect_mono}] RL monos
RLN (2,[@{thm rev_subsetD}]);
(*Minimizes backtracking by delivering the correct premise to each goal*) fun mutual_ind_tac _ [] 0 = all_tac
| mutual_ind_tac ctxt (prem::prems) i =
DETERM
(SELECT_GOAL
( (*Simplify the assumptions and goal by unfolding Part and using freeness of the Sum constructors; proves all but one
conjunct by contradiction*)
rewrite_goals_tac ctxt all_defs THEN
simp_tac (mut_ss |> Simplifier.add_simp @{thm Part_iff}) 1 THEN
IF_UNSOLVED (*simp_tac may have finished it off!*)
((*simplify assumptions*) (*some risk of excessive simplification here -- might have
to identify the bare minimum set of rewrites*)
full_simp_tac
(mut_ss |> Simplifier.add_simps (@{thms conj_simps} @ @{thms imp_simps} @ @{thms quant_simps})) 1 THEN (*unpackage and use "prem" in the corresponding place*)
REPEAT (resolve_tac ctxt @{thms impI} 1) THEN
resolve_tac ctxt [rewrite_rule ctxt all_defs prem] 1 THEN (*prem must not be REPEATed below: could loop!*)
DEPTH_SOLVE (FIRSTGOAL (ares_tac ctxt [@{thm impI}] ORELSE'
eresolve_tac ctxt (@{thm conjE} :: @{thm mp} :: cmonos))))
) i) THEN mutual_ind_tac ctxt prems (i-1);
val mutual_induct_fsplit = if need_mutual then
Goal.prove_global thy4 [] (map (induct_prem (rec_tms~~preds)) intr_tms)
mutual_induct_concl
(fn {context = ctxt, prems} => EVERY
[resolve_tac ctxt [quant_induct RS lemma] 1,
mutual_ind_tac ctxt (rev prems) (length prems)]) else @{thm TrueI};
(** Uncurrying the predicate in the ordinary induction rule **)
(*instantiate the variable to a tuple, if it is non-trivial, in order to allow the predicate to be "opened up".
The name "x.1" comes from the "RS spec" !*) val inst = case elem_frees of [_] => I
| _ => Drule.instantiate_normalize (TVars.empty,
Vars.make1 ((("x", 1), \<^Type>\<open>i\<close>), Thm.global_cterm_of thy4 elem_tuple));
(*strip quantifier and the implication*) val induct0 = inst (quant_induct RS @{thm spec} RSN (2, @{thm rev_mp}));
val \<^Const_>\<open>Trueprop for \<open>pred_var $ _\<close>\<close> = Thm.concl_of induct0
val induct0 =
CP.split_rule_var ctxt4
(pred_var, elem_type --> \<^Type>\<open>o\<close>, induct0)
|> Drule.export_without_context and mutual_induct = CP.remove_split ctxt4 mutual_induct_fsplit
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