Now distinguishes discrete from non-distrete types.
(* Title: Provers/Arith/fast_lin_arith.ML
ID: $Id$
Author: Tobias Nipkow
Copyright 1998 TU Munich
A generic linear arithmetic package.
It provides two tactics
lin_arith_tac: int -> tactic
cut_lin_arith_tac: thms -> int -> tactic
and a simplification procedure
lin_arith_prover: Sign.sg -> thm list -> term -> thm option
Only take premises and conclusions into account that are already (negated)
(in)equations. lin_arith_prover tries to prove or disprove the term.
*)
(*** Data needed for setting up the linear arithmetic package ***)
signature LIN_ARITH_LOGIC =
sig
val conjI: thm
val ccontr: thm (* (~ P ==> False) ==> P *)
val neqE: thm (* [| m ~= n; m < n ==> P; n < m ==> P |] ==> P *)
val notI: thm (* (P ==> False) ==> ~ P *)
val not_lessD: thm (* ~(m < n) ==> n <= m *)
val not_leD: thm (* ~(m <= n) ==> n < m *)
val sym: thm (* x = y ==> y = x *)
val mk_Eq: thm -> thm
val mk_Trueprop: term -> term
val neg_prop: term -> term
val is_False: thm -> bool
val is_nat: typ list * term -> bool
val mk_nat_thm: Sign.sg -> term -> thm
end;
(*
mk_Eq(~in) = `in == False'
mk_Eq(in) = `in == True'
where `in' is an (in)equality.
neg_prop(t) = neg if t is wrapped up in Trueprop and
nt is the (logically) negated version of t, where the negation
of a negative term is the term itself (no double negation!);
is_nat(parameter-types,t) = t:nat
mk_nat_thm(t) = "0 <= t"
*)
signature LIN_ARITH_DATA =
sig
val add_mono_thms: thm list ref
(* [| i rel1 j; m rel2 n |] ==> i + m rel3 j + n *)
val lessD: thm list ref (* m < n ==> m+1 <= n *)
val decomp:
term ->
((term * int)list * int * string * (term * int)list * int * bool)option
val simp: (thm -> thm) ref
end;
(*
decomp(`x Rel y') should yield (p,i,Rel,q,j,d)
where Rel is one of "<", "~<", "<=", "~<=" and "=" and
p/q is the decomposition of the sum terms x/y into a list
of summand * multiplicity pairs and a constant summand and
d indicates if the domain is discrete.
simp must reduce contradictory <= to False.
It should also cancel common summands to keep <= reduced;
otherwise <= can grow to massive proportions.
*)
signature FAST_LIN_ARITH =
sig
val lin_arith_prover: Sign.sg -> thm list -> term -> thm option
val lin_arith_tac: int -> tactic
val cut_lin_arith_tac: thm list -> int -> tactic
end;
functor Fast_Lin_Arith(structure LA_Logic:LIN_ARITH_LOGIC
and LA_Data:LIN_ARITH_DATA) : FAST_LIN_ARITH =
struct
(*** A fast decision procedure ***)
(*** Code ported from HOL Light ***)
(* possible optimizations:
use (var,coeff) rep or vector rep tp save space;
treat non-negative atoms separately rather than adding 0 <= atom
*)
datatype lineq_type = Eq | Le | Lt;
datatype injust = Asm of int
| Nat of int (* index of atom *)
| LessD of injust
| NotLessD of injust
| NotLeD of injust
| NotLeDD of injust
| Multiplied of int * injust
| Added of injust * injust;
datatype lineq = Lineq of int * lineq_type * int list * injust;
(* ------------------------------------------------------------------------- *)
(* Calculate new (in)equality type after addition. *)
(* ------------------------------------------------------------------------- *)
fun find_add_type(Eq,x) = x
| find_add_type(x,Eq) = x
| find_add_type(_,Lt) = Lt
| find_add_type(Lt,_) = Lt
| find_add_type(Le,Le) = Le;
(* ------------------------------------------------------------------------- *)
(* Multiply out an (in)equation. *)
(* ------------------------------------------------------------------------- *)
fun multiply_ineq n (i as Lineq(k,ty,l,just)) =
if n = 1 then i
else if n = 0 andalso ty = Lt then sys_error "multiply_ineq"
else if n < 0 andalso (ty=Le orelse ty=Lt) then sys_error "multiply_ineq"
else Lineq(n * k,ty,map (apl(n,op * )) l,Multiplied(n,just));
(* ------------------------------------------------------------------------- *)
(* Add together (in)equations. *)
(* ------------------------------------------------------------------------- *)
fun add_ineq (i1 as Lineq(k1,ty1,l1,just1)) (i2 as Lineq(k2,ty2,l2,just2)) =
let val l = map2 (op +) (l1,l2)
in Lineq(k1+k2,find_add_type(ty1,ty2),l,Added(just1,just2)) end;
(* ------------------------------------------------------------------------- *)
(* Elimination of variable between a single pair of (in)equations. *)
(* If they're both inequalities, 1st coefficient must be +ve, 2nd -ve. *)
(* ------------------------------------------------------------------------- *)
fun gcd x y =
let fun gxd x y =
if y = 0 then x else gxd y (x mod y)
in if x < y then gxd y x else gxd x y end;
fun lcm x y = (x * y) div gcd x y;
fun el 0 (h::_) = h
| el n (_::t) = el (n - 1) t
| el _ _ = sys_error "el";
fun elim_var v (i1 as Lineq(k1,ty1,l1,just1)) (i2 as Lineq(k2,ty2,l2,just2)) =
let val c1 = el v l1 and c2 = el v l2
val m = lcm (abs c1) (abs c2)
val m1 = m div (abs c1) and m2 = m div (abs c2)
val (n1,n2) =
if (c1 >= 0) = (c2 >= 0)
then if ty1 = Eq then (~m1,m2)
else if ty2 = Eq then (m1,~m2)
else sys_error "elim_var"
else (m1,m2)
val (p1,p2) = if ty1=Eq andalso ty2=Eq andalso (n1 = ~1 orelse n2 = ~1)
then (~n1,~n2) else (n1,n2)
in add_ineq (multiply_ineq n1 i1) (multiply_ineq n2 i2) end;
(* ------------------------------------------------------------------------- *)
(* The main refutation-finding code. *)
(* ------------------------------------------------------------------------- *)
fun is_trivial (Lineq(_,_,l,_)) = forall (fn i => i=0) l;
fun is_answer (ans as Lineq(k,ty,l,_)) =
case ty of Eq => k <> 0 | Le => k > 0 | Lt => k >= 0;
fun calc_blowup l =
let val (p,n) = partition (apl(0,op<)) (filter (apl(0,op<>)) l)
in (length p) * (length n) end;
(* ------------------------------------------------------------------------- *)
(* Main elimination code: *)
(* *)
(* (1) Looks for immediate solutions (false assertions with no variables). *)
(* *)
(* (2) If there are any equations, picks a variable with the lowest absolute *)
(* coefficient in any of them, and uses it to eliminate. *)
(* *)
(* (3) Otherwise, chooses a variable in the inequality to minimize the *)
(* blowup (number of consequences generated) and eliminates it. *)
(* ------------------------------------------------------------------------- *)
fun allpairs f xs ys =
flat(map (fn x => map (fn y => f x y) ys) xs);
fun extract_first p =
let fun extract xs (y::ys) = if p y then (Some y,xs@ys)
else extract (y::xs) ys
| extract xs [] = (None,xs)
in extract [] end;
fun print_ineqs ineqs =
writeln(cat_lines(""::map (fn Lineq(c,t,l,_) =>
string_of_int c ^
(case t of Eq => " = " | Lt=> " < " | Le => " <= ") ^
commas(map string_of_int l)) ineqs));
fun elim ineqs =
let (*val dummy = print_ineqs ineqs;*)
val (triv,nontriv) = partition is_trivial ineqs in
if not(null triv)
then case find_first is_answer triv of
None => elim nontriv | some => some
else
if null nontriv then None else
let val (eqs,noneqs) = partition (fn (Lineq(_,ty,_,_)) => ty=Eq) nontriv in
if not(null eqs) then
let val clist = foldl (fn (cs,Lineq(_,_,l,_)) => l union cs) ([],eqs)
val sclist = sort (fn (x,y) => int_ord(abs(x),abs(y)))
(filter (fn i => i<>0) clist)
val c = hd sclist
val (Some(eq as Lineq(_,_,ceq,_)),othereqs) =
extract_first (fn Lineq(_,_,l,_) => c mem l) eqs
val v = find_index (fn k => k=c) ceq
val (ioth,roth) = partition (fn (Lineq(_,_,l,_)) => el v l = 0)
(othereqs @ noneqs)
val others = map (elim_var v eq) roth @ ioth
in elim others end
else
let val lists = map (fn (Lineq(_,_,l,_)) => l) noneqs
val numlist = 0 upto (length(hd lists) - 1)
val coeffs = map (fn i => map (el i) lists) numlist
val blows = map calc_blowup coeffs
val iblows = blows ~~ numlist
val nziblows = filter (fn (i,_) => i<>0) iblows
in if null nziblows then None else
let val (c,v) = hd(sort (fn (x,y) => int_ord(fst(x),fst(y))) nziblows)
val (no,yes) = partition (fn (Lineq(_,_,l,_)) => el v l = 0) ineqs
val (pos,neg) = partition(fn (Lineq(_,_,l,_)) => el v l > 0) yes
in elim (no @ allpairs (elim_var v) pos neg) end
end
end
end;
(* ------------------------------------------------------------------------- *)
(* Translate back a proof. *)
(* ------------------------------------------------------------------------- *)
(* FIXME OPTIMIZE!!!!
Addition/Multiplication need i*t representation rather than t+t+...
Simplification may detect a contradiction 'prematurely' due to type
information: n+1 <= 0 is simplified to False and does not need to be crossed
with 0 <= n.
*)
local
exception FalseE of thm
in
fun mkthm sg asms just =
let val atoms = foldl (fn (ats,(lhs,_,_,rhs,_,_)) =>
map fst lhs union (map fst rhs union ats))
([], mapfilter (LA_Data.decomp o concl_of) asms)
fun addthms thm1 thm2 =
let val conj = thm1 RS (thm2 RS LA_Logic.conjI)
in the(get_first (fn th => Some(conj RS th) handle _ => None)
(!LA_Data.add_mono_thms))
end;
fun multn(n,thm) =
let fun mul(i,th) = if i=1 then th else mul(i-1, addthms thm th)
in if n < 0 then mul(~n,thm) RS LA_Logic.sym else mul(n,thm) end;
fun simp thm =
let val thm' = !LA_Data.simp thm
in if LA_Logic.is_False thm' then raise FalseE thm' else thm' end
fun mk(Asm i) = ((*writeln"Asm";prth*)(nth_elem(i,asms)))
| mk(Nat(i)) = ((*writeln"N";LA_Logic.mk_nat_thm sg (nth_elem(i,atoms)))
| mk(LessD(j)) = ((*writeln"L";prth*)(hd([mk j] RL !LA_Data.lessD)))
| mk(NotLeD(j)) = ((*writeln"NLe";prth*)(mk j RS LA_Logic.not_leD))
| mk(NotLeDD(j)) = ((*writeln"NLeD";prth*)(hd([mk j RS LA_Logic.not_leD] RL !LA_Data.lessD)))
| mk(NotLessD(j)) = ((*writeln"NL";prth*)(mk j RS LA_Logic.not_lessD))
| mk(Added(j1,j2)) = ((*writeln"+";prth*)(simp(prth(addthms (mk j1) (mk j2)))))
| mk(Multiplied(n,j)) = ((*writeln"*";multn(n,mk j))
in (*writeln"mkthm";*)!LA_Data.simp(mk just) handle FalseE thm => thm end
end;
fun coeff poly atom = case assoc(poly,atom) of None => 0 | Some i => i;
fun mklineq atoms =
let val n = length atoms in
fn ((lhs,i,rel,rhs,j,discrete),k) =>
let val lhsa = map (coeff lhs) atoms
and rhsa = map (coeff rhs) atoms
val diff = map2 (op -) (rhsa,lhsa)
val c = i-j
val just = Asm k
in case rel of
"<=" => Some(Lineq(c,Le,diff,just))
| "~<=" => if discrete
then Some(Lineq(1-c,Le,map (op ~) diff,NotLeDD(just)))
else Some(Lineq(~c,Lt,map (op ~) diff,NotLeD(just)))
| "<" => if discrete
then Some(Lineq(c+1,Le,diff,LessD(just)))
else Some(Lineq(c,Lt,diff,just))
| "~<" => Some(Lineq(~c,Le,map (op~) diff,NotLessD(just)))
| "=" => Some(Lineq(c,Eq,diff,just))
| "~=" => None
| _ => sys_error("mklineq" ^ rel)
end
end;
fun mknat pTs ixs (atom,i) =
if LA_Logic.is_nat(pTs,atom)
then let val l = map (fn j => if j=i then 1 else 0) ixs
in Some(Lineq(0,Le,l,Nat(i))) end
else None
fun abstract pTs items =
let val atoms = foldl (fn (ats,((lhs,_,_,rhs,_,_),_)) =>
(map fst lhs) union ((map fst rhs) union ats))
([],items)
val ixs = 0 upto (length(atoms)-1)
val iatoms = atoms ~~ ixs
in mapfilter (mklineq atoms) items @ mapfilter (mknat pTs ixs) iatoms end;
(* Ordinary refutation *)
fun refute1(pTs,items) =
(case elim (abstract pTs items) of
None => []
| Some(Lineq(_,_,_,j)) => [j]);
fun refute1_tac(i,just) =
fn state =>
let val sg = #sign(rep_thm state)
in resolve_tac [LA_Logic.notI,LA_Logic.ccontr] i THEN
METAHYPS (fn asms => rtac (mkthm sg asms just) 1) i
end
state;
(* Double refutation caused by equality in conclusion *)
fun refute2(pTs,items, (rhs,i,_,lhs,j,d), nHs) =
(case elim (abstract pTs (items@[((rhs,i,"<",lhs,j,d),nHs)])) of
None => []
| Some(Lineq(_,_,_,j1)) =>
(case elim (abstract pTs (items@[((lhs,j,"<",rhs,i,d),nHs)])) of
None => []
| Some(Lineq(_,_,_,j2)) => [j1,j2]));
fun refute2_tac(i,just1,just2) =
fn state =>
let val sg = #sign(rep_thm state)
in rtac LA_Logic.ccontr i THEN rotate_tac ~1 i THEN etac LA_Logic.neqE i THEN
METAHYPS (fn asms => rtac (mkthm sg asms just1) 1) i THEN
METAHYPS (fn asms => rtac (mkthm sg asms just2) 1) i
end
state;
fun prove(pTs,Hs,concl) =
let val nHs = length Hs
val ixHs = Hs ~~ (0 upto (nHs-1))
val Hitems = mapfilter (fn (h,i) => case LA_Data.decomp h of
None => None | Some(it) => Some(it,i)) ixHs
in case LA_Data.decomp concl of
None => if null Hitems then [] else refute1(pTs,Hitems)
| Some(citem as (r,i,rel,l,j,d)) =>
if rel = "="
then refute2(pTs,Hitems,citem,nHs)
else let val neg::rel0 = explode rel
val nrel = if neg = "~" then implode rel0 else "~"^rel
in refute1(pTs, Hitems@[((r,i,nrel,l,j,d),nHs)]) end
end;
(*
Fast but very incomplete decider. Only premises and conclusions
that are already (negated) (in)equations are taken into account.
*)
val lin_arith_tac = SUBGOAL (fn (A,n) =>
let val pTs = rev(map snd (Logic.strip_params A))
val Hs = Logic.strip_assums_hyp A
val concl = Logic.strip_assums_concl A
in case prove(pTs,Hs,concl) of
[j] => refute1_tac(n,j)
| [j1,j2] => refute2_tac(n,j1,j2)
| _ => no_tac
end);
fun cut_lin_arith_tac thms i = cut_facts_tac thms i THEN lin_arith_tac i;
fun prover1(just,sg,thms,concl,pos) =
let val nconcl = LA_Logic.neg_prop concl
val cnconcl = cterm_of sg nconcl
val Fthm = mkthm sg (thms @ [assume cnconcl]) just
val contr = if pos then LA_Logic.ccontr else LA_Logic.notI
in Some(LA_Logic.mk_Eq ((implies_intr cnconcl Fthm) COMP contr)) end
handle _ => None;
(* handle thm with equality conclusion *)
fun prover2(just1,just2,sg,thms,concl) =
let val nconcl = LA_Logic.neg_prop concl (* m ~= n *)
val cnconcl = cterm_of sg nconcl
val neqthm = assume cnconcl
val casethm = neqthm COMP LA_Logic.neqE (* [|m<n ==> R; n<m ==> R|] ==> R *)
val [lessimp1,lessimp2] = prems_of casethm
val less1 = fst(Logic.dest_implies lessimp1) (* m<n *)
and less2 = fst(Logic.dest_implies lessimp2) (* n<m *)
val cless1 = cterm_of sg less1 and cless2 = cterm_of sg less2
val thm1 = mkthm sg (thms @ [assume cless1]) just1
and thm2 = mkthm sg (thms @ [assume cless2]) just2
val dthm1 = implies_intr cless1 thm1 and dthm2 = implies_intr cless2 thm2
val thm = dthm2 COMP (dthm1 COMP casethm)
in Some(LA_Logic.mk_Eq ((implies_intr cnconcl thm) COMP LA_Logic.ccontr)) end
handle _ => None;
(* PRE: concl is not negated! *)
fun lin_arith_prover sg thms concl =
let val Hs = map (#prop o rep_thm) thms
val Tconcl = LA_Logic.mk_Trueprop concl
in case prove([],Hs,Tconcl) of
[j] => prover1(j,sg,thms,Tconcl,true)
| [j1,j2] => prover2(j1,j2,sg,thms,Tconcl)
| _ => let val nTconcl = LA_Logic.neg_prop Tconcl
in case prove([],Hs,nTconcl) of
[j] => prover1(j,sg,thms,nTconcl,false)
(* [_,_] impossible because of negation *)
| _ => None
end
end;
end;