author  wenzelm 
Mon, 16 Feb 2009 21:23:33 +0100  
changeset 29758  7a3b5bbed313 
parent 23058  c722004c5a22 
child 35762  af3ff2ba4c54 
permissions  rwrr 
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(* Title: Provers/Arith/combine_numerals.ML 
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ID: $Id$ 
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Author: Lawrence C Paulson, Cambridge University Computer Laboratory 
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Copyright 2000 University of Cambridge 
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Combine coefficients in expressions: 
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i + #m*u + j ... + #n*u + k == #(m+n)*u + (i + (j + k)) 
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It works by (a) massaging the sum to bring the selected terms to the front: 
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#m*u + (#n*u + (i + (j + k))) 
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(b) then using left_distrib to reach 
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#(m+n)*u + (i + (j + k)) 
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*) 
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signature COMBINE_NUMERALS_DATA = 
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sig 
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(*abstract syntax*) 
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eqtype coeff 
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val iszero: coeff > bool 
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val add: coeff * coeff > coeff (*addition (or multiplication) *) 
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Polymorphic treatment of binary arithmetic using axclasses
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val mk_sum: typ > term list > term 
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val dest_sum: term > term list 
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val mk_coeff: coeff * term > term 
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val dest_coeff: term > coeff * term 
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(*rules*) 
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val left_distrib: thm 
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(*proof tools*) 
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val prove_conv: tactic list > Proof.context > term * term > thm option 
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val trans_tac: simpset > thm option > tactic (*applies the initial lemma*) 
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val norm_tac: simpset > tactic (*proves the initial lemma*) 

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val numeral_simp_tac: simpset > tactic (*proves the final theorem*) 

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val simplify_meta_eq: simpset > thm > thm (*simplifies the final theorem*) 

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end; 
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functor CombineNumeralsFun(Data: COMBINE_NUMERALS_DATA): 
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sig 
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val proc: simpset > term > thm option 
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end 
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= 
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struct 
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(*Remove the first occurrence of #m*u from the term list*) 
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fun remove (_, _, []) = (*impossible, since #m*u was found by find_repeated*) 
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raise TERM("combine_numerals: remove", []) 
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 remove (m, u, t::terms) = 
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case try Data.dest_coeff t of 
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SOME(n,v) => if m=n andalso u aconv v then terms 
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else t :: remove (m, u, terms) 
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 NONE => t :: remove (m, u, terms); 
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(*a lefttoright scan of terms, seeking another term of the form #n*u, where 
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#m*u is already in terms for some m*) 
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fun find_repeated (tab, _, []) = raise TERM("find_repeated", []) 
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 find_repeated (tab, past, t::terms) = 
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case try Data.dest_coeff t of 
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SOME(n,u) => 
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(case Termtab.lookup tab u of 
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SOME m => (u, m, n, rev (remove (m,u,past)) @ terms) 
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 NONE => find_repeated (Termtab.update (u, n) tab, 
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t::past, terms)) 
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 NONE => find_repeated (tab, t::past, terms); 
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(*the simplification procedure*) 
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fun proc ss t = 
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let 
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val ctxt = Simplifier.the_context ss; 
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val ([t'], ctxt') = Variable.import_terms true [t] ctxt 
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val export = singleton (Variable.export ctxt' ctxt) 
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val (u,m,n,terms) = find_repeated (Termtab.empty, [], Data.dest_sum t') 
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val T = Term.fastype_of u 
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val reshape = (*Move i*u to the front and put j*u into standard form 
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i + #m + j + k == #m + i + (j + k) *) 
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if Data.iszero m orelse Data.iszero n then (*trivial, so do nothing*) 
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raise TERM("combine_numerals", []) 
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else Data.prove_conv [Data.norm_tac ss] ctxt 
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(t', Data.mk_sum T ([Data.mk_coeff (m, u), Data.mk_coeff (n, u)] @ terms)) 
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in 
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Option.map (export o Data.simplify_meta_eq ss) 
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(Data.prove_conv 
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[Data.trans_tac ss reshape, rtac Data.left_distrib 1, 
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Data.numeral_simp_tac ss] ctxt 
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(t', Data.mk_sum T (Data.mk_coeff(Data.add(m,n), u) :: terms))) 
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end 
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(* FIXME avoid handling of generic exceptions *) 
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handle TERM _ => NONE 
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 TYPE _ => NONE; (*Typically (if thy doesn't include Numeral) 

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Undeclared type constructor "Numeral.bin"*) 
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end; 