From: ajreynol Date: Thu, 21 Jul 2016 15:56:09 +0000 (-0500) Subject: Fixes for strings, explanations for constant split propagations, substr under concat... X-Git-Tag: cvc5-1.0.0~6040^2~34^2~1 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=b5956e457da61e4d49cd35e0a73ba423230a25e0;p=cvc5.git Fixes for strings, explanations for constant split propagations, substr under concat rewrite. Avoid duplicate re.range length lemmas. --- diff --git a/src/theory/strings/theory_strings.cpp b/src/theory/strings/theory_strings.cpp index 774926315..cdcac7604 100644 --- a/src/theory/strings/theory_strings.cpp +++ b/src/theory/strings/theory_strings.cpp @@ -75,6 +75,7 @@ TheoryStrings::TheoryStrings(context::Context* c, context::UserContext* u, d_preproc(u), d_preproc_cache(u), d_extf_infer_cache(c), + d_extf_infer_cache_u(u), d_ee_disequalities(c), d_congruent(c), d_proxy_var(u), @@ -937,10 +938,21 @@ void TheoryStrings::assertPendingFact(Node atom, bool polarity, Node exp) { d_equalityEngine.assertEquality( atom, polarity, exp ); Trace("strings-pending-debug") << " Finished assert equality" << std::endl; } else { - if( atom.getKind()==kind::STRING_IN_REGEXP ) { + d_equalityEngine.assertPredicate( atom, polarity, exp ); + //process extf + if( atom.getKind()==kind::STRING_IN_REGEXP ){ addExtendedFuncTerm( atom ); + if( polarity && atom[1].getKind()==kind::REGEXP_RANGE ){ + if( d_extf_infer_cache_u.find( atom )==d_extf_infer_cache_u.end() ){ + d_extf_infer_cache_u.insert( atom ); + //length of first argument is one + Node conc = d_one.eqNode( NodeManager::currentNM()->mkNode( kind::STRING_LENGTH, atom[0] ) ); + Node lem = NodeManager::currentNM()->mkNode( kind::OR, atom.negate(), conc ); + Trace("strings-lemma") << "Strings::Lemma RE-Range-Len : " << lem << std::endl; + d_out->lemma( lem ); + } + } } - d_equalityEngine.assertPredicate( atom, polarity, exp ); } Trace("strings-pending-debug") << " Now collect terms" << std::endl; //collect extended function terms in the atom @@ -1426,16 +1438,7 @@ void TheoryStrings::checkExtfInference( Node n, Node nr, ExtfInfoTmp& in, int ef //d_extf_infer_cache stores whether we have made the inferences associated with a node n, // this may need to be generalized if multiple inferences apply - if( nr.getKind()==kind::STRING_IN_REGEXP ){ - if( in.d_pol==1 && nr[1].getKind()==kind::REGEXP_RANGE ){ - if( d_extf_infer_cache.find( nr )==d_extf_infer_cache.end() ){ - d_extf_infer_cache.insert( nr ); - //length of first argument is one - Node conc = d_one.eqNode( NodeManager::currentNM()->mkNode(kind::STRING_LENGTH, nr[0]) ); - sendInference( in.d_exp, conc, "RE-Range-Len", true ); - } - } - }else if( nr.getKind()==kind::STRING_STRCTN ){ + if( nr.getKind()==kind::STRING_STRCTN ){ if( ( in.d_pol==1 && nr[1].getKind()==kind::STRING_CONCAT ) || ( in.d_pol==-1 && nr[0].getKind()==kind::STRING_CONCAT ) ){ if( d_extf_infer_cache.find( nr )==d_extf_infer_cache.end() ){ d_extf_infer_cache.insert( nr ); @@ -2019,44 +2022,27 @@ bool TheoryStrings::normalizeEquivalenceClass( Node eqc ) { } } //construct the normal form - if( normal_forms.empty() ){ - Trace("strings-solve-debug2") << "construct the normal form" << std::endl; - //FIXME: cleanup - eq::EqClassIterator eqc_i = eq::EqClassIterator( eqc, &d_equalityEngine ); - Node eqc_c = eqc; - //do not choose a concat here (in this case they have non-trivial explanation why they normalize to self) - while( eqc_c.getKind()==kind::STRING_CONCAT && !eqc_i.isFinished() ){ - Node n = (*eqc_i); - if( d_congruent.find( n )==d_congruent.end() ){ - if( n.getKind()!=kind::STRING_CONCAT ){ - eqc_c = n; - } - } - ++eqc_i; - } - getConcatVec( eqc_c, d_normal_forms[eqc] ); - d_normal_forms_base[eqc] = eqc_c; + Assert( !normal_forms.empty() ); + + int nf_index = 0; + std::vector< Node >::iterator itn = std::find( normal_form_src.begin(), normal_form_src.end(), eqc ); + if( itn!=normal_form_src.end() ){ + nf_index = itn - normal_form_src.begin(); + Trace("strings-solve-debug2") << "take normal form " << nf_index << std::endl; + Assert( normal_form_src[nf_index]==eqc ); }else{ - int nf_index = 0; - std::vector< Node >::iterator itn = std::find( normal_form_src.begin(), normal_form_src.end(), eqc ); - if( itn!=normal_form_src.end() ){ - nf_index = itn - normal_form_src.begin(); - Trace("strings-solve-debug2") << "take normal form " << nf_index << std::endl; - Assert( normal_form_src[nf_index]==eqc ); - }else{ - //just take the first normal form - Trace("strings-solve-debug2") << "take the first normal form" << std::endl; - } - d_normal_forms[eqc].insert( d_normal_forms[eqc].end(), normal_forms[nf_index].begin(), normal_forms[nf_index].end() ); - d_normal_forms_exp[eqc].insert( d_normal_forms_exp[eqc].end(), normal_forms_exp[nf_index].begin(), normal_forms_exp[nf_index].end() ); - Trace("strings-solve-debug2") << "take normal form ... done" << std::endl; - d_normal_forms_base[eqc] = normal_form_src[nf_index]; - //track dependencies - for( unsigned i=0; i Node nn = nf_n.size()==0 ? d_emptyString : nf_n[0]; Assert( areEqual( nn, eqc ) ); } + }else{ + eqc_non_c = n; } } ++eqc_i; } - if( !normal_forms.empty() ) { + if( normal_forms.empty() ) { + Trace("strings-solve-debug2") << "construct the normal form" << std::endl; + //do not choose a concat here use "eqc_non_c" (in this case they have non-trivial explanation why they normalize to self) + std::vector< Node > eqc_non_c_nf; + getConcatVec( eqc_non_c, eqc_non_c_nf ); + normal_forms.push_back( eqc_non_c_nf ); + normal_form_src.push_back( eqc_non_c ); + normal_forms_exp.push_back( std::vector< Node >() ); + normal_forms_exp_depend.push_back( std::map< Node, std::map< bool, int > >() ); + }else{ if(Trace.isOn("strings-solve")) { Trace("strings-solve") << "--- Normal forms for equivlance class " << eqc << " : " << std::endl; for( unsigned i=0; i return true; } -void TheoryStrings::getExplanationVectorForPrefix( std::vector< std::vector< Node > > &normal_forms, std::vector< Node > &normal_form_src, - std::vector< std::vector< Node > > &normal_forms_exp, std::vector< std::map< Node, std::map< bool, int > > >& normal_forms_exp_depend, - unsigned i, unsigned j, int index, bool isRev, std::vector< Node >& curr_exp ) { +void TheoryStrings::getExplanationVectorForPrefix( std::vector< std::vector< Node > > &normal_forms_exp, std::vector< std::map< Node, std::map< bool, int > > >& normal_forms_exp_depend, + unsigned i, int index, bool isRev, std::vector< Node >& curr_exp ) { if( index==-1 || !options::stringMinPrefixExplain() ){ curr_exp.insert(curr_exp.end(), normal_forms_exp[i].begin(), normal_forms_exp[i].end() ); - curr_exp.insert(curr_exp.end(), normal_forms_exp[j].begin(), normal_forms_exp[j].end() ); }else{ - Trace("strings-explain-prefix") << "Get explanation for prefix " << index << " of normal forms " << i << " and " << j << ", reverse = " << isRev << std::endl; - for( unsigned r=0; r<2; r++ ){ - int tindex = r==0 ? i : j; - for( unsigned k=0; k > &normal_forms, std::vector< Node > &normal_form_src, + std::vector< std::vector< Node > > &normal_forms_exp, std::vector< std::map< Node, std::map< bool, int > > >& normal_forms_exp_depend, + unsigned i, unsigned j, int index_i, int index_j, bool isRev, std::vector< Node >& curr_exp ) { + Trace("strings-explain-prefix") << "Get explanation for prefix " << index_i << ", " << index_j << " of normal forms " << i << " and " << j << ", reverse = " << isRev << std::endl; + for( unsigned r=0; r<2; r++ ){ + getExplanationVectorForPrefix( normal_forms_exp, normal_forms_exp_depend, r==0 ? i : j, r==0 ? index_i : index_j, isRev, curr_exp ); } + Trace("strings-explain-prefix") << "Included " << curr_exp.size() << " / " << ( normal_forms_exp[i].size() + normal_forms_exp[j].size() ) << std::endl; + addToExplanation( normal_form_src[i], normal_form_src[j], curr_exp ); } bool TheoryStrings::processNEqc( std::vector< std::vector< Node > > &normal_forms, std::vector< Node > &normal_form_src, @@ -2318,7 +2317,7 @@ bool TheoryStrings::processNEqc( std::vector< std::vector< Node > > &normal_form c_loop_index = loop_in_i!=-1 ? loop_in_i : loop_in_j; c_index = index; - getExplanationVectorForPrefix( normal_forms, normal_form_src, normal_forms_exp, normal_forms_exp_depend, i, j, -1, false, c_lb_exp ); + getExplanationVectorForPrefixEq( normal_forms, normal_form_src, normal_forms_exp, normal_forms_exp_depend, i, j, -1, -1, false, c_lb_exp ); if(options::stringLB() == 0) { flag_lb = true; @@ -2341,13 +2340,15 @@ bool TheoryStrings::processNEqc( std::vector< std::vector< Node > > &normal_form Assert( other_str.getKind()!=kind::STRING_CONCAT, "Other string is not CONCAT." ); if( !d_equalityEngine.areDisequal(other_str, d_emptyString, true) ) { sendSplit( other_str, d_emptyString, "Len-Split(CST)" ); - } else { - Assert(areDisequal(other_str, d_emptyString), "CST Split on empty Var"); - getExplanationVectorForPrefix( normal_forms, normal_form_src, normal_forms_exp, normal_forms_exp_depend, i, j, index, false, antec ); + }else{ + Assert(areDisequal(other_str, d_emptyString), "CST Split on empty Var"); Node xnz = other_str.eqNode(d_emptyString).negate(); antec.push_back( xnz ); Node conc; if( normal_forms[nconst_k].size() > index + 1 && normal_forms[nconst_k][index + 1].isConst() ) { + int index_i = const_k==i ? index : index+1; + int index_j = const_k==j ? index : index+1; + getExplanationVectorForPrefixEq( normal_forms, normal_form_src, normal_forms_exp, normal_forms_exp_depend, i, j, index_i, index_j, false, antec ); CVC4::String stra = const_str.getConst(); CVC4::String strb = normal_forms[nconst_k][index + 1].getConst(); CVC4::String stra1 = stra.substr(1); @@ -2358,22 +2359,36 @@ bool TheoryStrings::processNEqc( std::vector< std::vector< Node > > &normal_form Node sk = mkSkolemCached( other_str, prea, sk_id_c_spt, "c_spt" ); conc = other_str.eqNode( mkConcat(prea, sk) ); Trace("strings-csp") << "Const Split: " << prea << " is removed from " << stra << " due to " << strb << std::endl; + sendInference( antec, conc, "S-Split(CST-P)-prop", true ); } else { + getExplanationVectorForPrefixEq( normal_forms, normal_form_src, normal_forms_exp, normal_forms_exp_depend, i, j, index, index, false, antec ); + /* TODO + CVC4::String stra = const_str.getConst(); + if( stra.size()>3 ){ + //split string in half + Node c_firstHalf = NodeManager::currentNM()->mkConst( stra.substr(0, stra.size()/2 ) ); + Node sk = mkSkolemCached( other_str, c_firstHalf , sk_id_vc_bin_spt, "c_spt" ); + conc = NodeManager::currentNM()->mkNode( kind::OR, other_str.eqNode( NodeManager::currentNM()->mkNode( kind::STRING_CONCAT, c_firstHalf, sk ) ), + NodeManager::currentNM()->mkNode( kind::AND, + sk.eqNode( d_emptyString ).negate(), + c_firstHalf.eqNode( NodeManager::currentNM()->mkNode( kind::STRING_CONCAT, other_str, sk ) ) )); + Trace("strings-csp") << "Const Split: " << c_firstHalf << " is removed from " << const_str << " (binary) " << std::endl; + sendInference( antec, conc, "S-Split(CST-P)-binary", true ); + }else{ + */ // normal v/c split Node firstChar = const_str.getConst().size() == 1 ? const_str : NodeManager::currentNM()->mkConst( const_str.getConst().substr(0, 1) ); Node sk = mkSkolemCached( other_str, firstChar, sk_id_vc_spt, "c_spt" ); conc = other_str.eqNode( mkConcat(firstChar, sk) ); - Trace("strings-csp") << "Const Split: " << firstChar << " is removed from " << const_str << " (normal) " << std::endl; + Trace("strings-csp") << "Const Split: " << firstChar << " is removed from " << const_str << " (serial) " << std::endl; + sendInference( antec, conc, "S-Split(CST-P)", true ); } - - conc = Rewriter::rewrite( conc ); - sendInference( antec, conc, "S-Split(CST-P)", true ); } return true; } else { std::vector< Node > antec_new_lits; - getExplanationVectorForPrefix( normal_forms, normal_form_src, normal_forms_exp, normal_forms_exp_depend, i, j, index, false, antec ); + getExplanationVectorForPrefixEq( normal_forms, normal_form_src, normal_forms_exp, normal_forms_exp_depend, i, j, index, index, false, antec ); Node ldeq = NodeManager::currentNM()->mkNode( kind::EQUAL, length_term_i, length_term_j ).negate(); if( d_equalityEngine.areDisequal( length_term_i, length_term_j, true ) ){ @@ -2472,7 +2487,7 @@ bool TheoryStrings::processSimpleNEq( std::vector< std::vector< Node > > &normal unsigned index_k = index; //Node eq_exp = mkAnd( curr_exp ); std::vector< Node > curr_exp; - getExplanationVectorForPrefix( normal_forms, normal_form_src, normal_forms_exp, normal_forms_exp_depend, i, j, -1, isRev, curr_exp ); + getExplanationVectorForPrefixEq( normal_forms, normal_form_src, normal_forms_exp, normal_forms_exp_depend, i, j, -1, -1, isRev, curr_exp ); while(!d_conflict && index_k > &normal //eq = Rewriter::rewrite( eq ); Node length_eq = length_term_i.eqNode( length_term_j ); //temp_exp.insert(temp_exp.end(), curr_exp.begin(), curr_exp.end() ); - getExplanationVectorForPrefix( normal_forms, normal_form_src, normal_forms_exp, normal_forms_exp_depend, i, j, index, isRev, temp_exp ); + getExplanationVectorForPrefixEq( normal_forms, normal_form_src, normal_forms_exp, normal_forms_exp_depend, i, j, index, index, isRev, temp_exp ); temp_exp.push_back(length_eq); sendInference( temp_exp, eq, "N_Unify" ); return true; @@ -2511,7 +2526,7 @@ bool TheoryStrings::processSimpleNEq( std::vector< std::vector< Node > > &normal Node conc; std::vector< Node > antec; //antec.insert(antec.end(), curr_exp.begin(), curr_exp.end() ); - getExplanationVectorForPrefix( normal_forms, normal_form_src, normal_forms_exp, normal_forms_exp_depend, i, j, -1, isRev, antec ); + getExplanationVectorForPrefixEq( normal_forms, normal_form_src, normal_forms_exp, normal_forms_exp_depend, i, j, -1, -1, isRev, antec ); std::vector< Node > eqn; for( unsigned r=0; r<2; r++ ) { int index_k = index; @@ -2562,7 +2577,7 @@ bool TheoryStrings::processSimpleNEq( std::vector< std::vector< Node > > &normal std::vector< Node > antec; //curr_exp is conflict //antec.insert(antec.end(), curr_exp.begin(), curr_exp.end() ); - getExplanationVectorForPrefix( normal_forms, normal_form_src, normal_forms_exp, normal_forms_exp_depend, i, j, index, isRev, antec ); + getExplanationVectorForPrefixEq( normal_forms, normal_form_src, normal_forms_exp, normal_forms_exp_depend, i, j, index, index, isRev, antec ); sendInference( antec, d_false, "N_Const", true ); return true; } @@ -3448,9 +3463,10 @@ void TheoryStrings::checkLengthsEqc() { ant.insert( ant.end(), d_normal_forms_exp[d_strings_eqc[i]].begin(), d_normal_forms_exp[d_strings_eqc[i]].end() ); ant.push_back( d_normal_forms_base[d_strings_eqc[i]].eqNode( lt ) ); Node lc = NodeManager::currentNM()->mkNode( kind::STRING_LENGTH, nf ); - lc = Rewriter::rewrite( lc ); - Node eq = llt.eqNode( lc ); - if( llt!=lc ){ + Node lcr = Rewriter::rewrite( lc ); + Trace("strings-process-debug") << "Rewrote length " << lc << " to " << lcr << std::endl; + Node eq = llt.eqNode( lcr ); + if( llt!=lcr ){ ei->d_normalized_length.set( eq ); sendInference( ant, eq, "LEN-NORM", true ); } @@ -4293,7 +4309,7 @@ void TheoryStrings::checkMemberships() { antec = Rewriter::rewrite( NodeManager::currentNM()->mkNode(kind::AND, antec, mkExplain(rnfexp)) ); Node conc = nvec.size()==1 ? nvec[0] : NodeManager::currentNM()->mkNode(kind::AND, nvec); conc = Rewriter::rewrite(conc); - sendLemma( antec, conc, "REGEXP" ); + sendLemma( antec, conc, "REGEXP_Unfold" ); addedLemma = true; if(changed) { cprocessed.push_back( assertion ); @@ -4301,7 +4317,7 @@ void TheoryStrings::checkMemberships() { processed.push_back( assertion ); } //d_regexp_ucached[assertion] = true; - } else { + }else{ Trace("strings-regexp") << "Unroll/simplify membership of non-atomic term " << xr << " = "; for( unsigned j=0; j d_empty_vec; // NodeList d_ee_disequalities; @@ -321,10 +322,11 @@ private: int processReverseDeq( std::vector< Node >& nfi, std::vector< Node >& nfj, Node ni, Node nj ); int processSimpleDeq( std::vector< Node >& nfi, std::vector< Node >& nfj, Node ni, Node nj, unsigned& index, bool isRev ); void checkDeqNF(); - - void getExplanationVectorForPrefix( std::vector< std::vector< Node > > &normal_forms, std::vector< Node > &normal_form_src, - std::vector< std::vector< Node > > &normal_forms_exp, std::vector< std::map< Node, std::map< bool, int > > >& normal_forms_exp_depend, - unsigned i, unsigned j, int index, bool isRev, std::vector< Node >& curr_exp ); + void getExplanationVectorForPrefix( std::vector< std::vector< Node > > &normal_forms_exp, std::vector< std::map< Node, std::map< bool, int > > >& normal_forms_exp_depend, + unsigned i, int index, bool isRev, std::vector< Node >& curr_exp ); + void getExplanationVectorForPrefixEq( std::vector< std::vector< Node > > &normal_forms, std::vector< Node > &normal_form_src, + std::vector< std::vector< Node > > &normal_forms_exp, std::vector< std::map< Node, std::map< bool, int > > >& normal_forms_exp_depend, + unsigned i, unsigned j, int index_i, int index_j, bool isRev, std::vector< Node >& curr_exp ); //check membership constraints Node mkRegExpAntec(Node atom, Node ant); @@ -401,6 +403,7 @@ protected: enum { sk_id_c_spt, sk_id_vc_spt, + sk_id_vc_bin_spt, sk_id_v_spt, sk_id_ctn_pre, sk_id_ctn_post, diff --git a/src/theory/strings/theory_strings_rewriter.cpp b/src/theory/strings/theory_strings_rewriter.cpp index bb03d8d0f..77caf8237 100644 --- a/src/theory/strings/theory_strings_rewriter.cpp +++ b/src/theory/strings/theory_strings_rewriter.cpp @@ -1032,16 +1032,16 @@ RewriteResponse TheoryStringsRewriter::postRewrite(TNode node) { Node tmpNode = rewriteConcatString(node[0]); if(tmpNode.isConst()) { retNode = NodeManager::currentNM()->mkConst( ::CVC4::Rational( tmpNode.getConst().size() ) ); - } else if(tmpNode.getKind() == kind::STRING_SUBSTR) { + //} else if(tmpNode.getKind() == kind::STRING_SUBSTR) { //retNode = tmpNode[2]; - } else { + } else if( tmpNode.getKind()==kind::STRING_CONCAT ){ // it has to be string concat std::vector node_vec; for(unsigned int i=0; imkConst( ::CVC4::Rational( tmpNode[i].getConst().size() ) ) ); - } else if(tmpNode[i].getKind() == kind::STRING_SUBSTR) { - node_vec.push_back( tmpNode[i][2] ); + //} else if(tmpNode[i].getKind() == kind::STRING_SUBSTR) { + // node_vec.push_back( tmpNode[i][2] ); } else { node_vec.push_back( NodeManager::currentNM()->mkNode(kind::STRING_LENGTH, tmpNode[i]) ); } diff --git a/test/regress/regress0/strings/Makefile.am b/test/regress/regress0/strings/Makefile.am index b09377bf7..9d7e9e13e 100644 --- a/test/regress/regress0/strings/Makefile.am +++ b/test/regress/regress0/strings/Makefile.am @@ -82,7 +82,9 @@ TESTS = \ cmu-disagree-0707-dd.smt2 \ cmu-5042-0707-2.smt2 \ cmu-dis-0707-3.smt2 \ - nf-ff-contains-abs.smt2 + nf-ff-contains-abs.smt2 \ + csp-prefix-exp-bug.smt2 \ + cmu-substr-rw.smt2 FAILING_TESTS = diff --git a/test/regress/regress0/strings/cmu-substr-rw.smt2 b/test/regress/regress0/strings/cmu-substr-rw.smt2 new file mode 100644 index 000000000..20bf979dd --- /dev/null +++ b/test/regress/regress0/strings/cmu-substr-rw.smt2 @@ -0,0 +1,12 @@ +(set-logic ALL_SUPPORTED) +(set-info :status sat) +(set-option :strings-exp true) +;(set-option :produce-models true) +;(set-option :rewrite-divk true) + +(declare-fun uri () String) + +(assert (and (and (and (and (and (and (and (and (and (and (and (and (not (not (= (ite (= (str.len (str.substr (str.substr uri (+ (str.indexof uri "%" 0) 1) (- (str.len uri) (+ (str.indexof uri "%" 0) 1))) 0 (- 2 0))) 2) 1 0) 0))) (not (not (= (ite (str.contains (str.substr uri (+ (str.indexof uri "%" 0) 1) (- (str.len uri) (+ (str.indexof uri "%" 0) 1))) "%") 1 0) 0)))) (not (not (= (ite (= (str.len (str.substr uri (+ (str.indexof uri "%" 0) 1) (- (str.len uri) (+ (str.indexof uri "%" 0) 1)))) 0) 1 0) 0)))) (not (= (ite (str.contains uri "%") 1 0) 0))) (not (not (= (ite (= (str.len uri) 0) 1 0) 0)))) (>= (+ (str.indexof uri "%" 0) 1) 0)) (>= (- (str.len uri) (+ (str.indexof uri "%" 0) 1)) 0)) (>= 0 0)) (>= (- 2 0) 0)) (>= (+ (str.indexof uri "%" 0) 1) 0)) (>= (- (str.len uri) (+ (str.indexof uri "%" 0) 1)) 0)) (>= (+ (str.indexof uri "%" 0) 1) 0)) (>= (- (str.len uri) (+ (str.indexof uri "%" 0) 1)) 0))) + +(check-sat) + diff --git a/test/regress/regress0/strings/csp-prefix-exp-bug.smt2 b/test/regress/regress0/strings/csp-prefix-exp-bug.smt2 new file mode 100644 index 000000000..c2fb4175c --- /dev/null +++ b/test/regress/regress0/strings/csp-prefix-exp-bug.smt2 @@ -0,0 +1,10 @@ +(set-logic QF_S) +(set-info :status sat) + +(declare-fun x () String) +(declare-fun y () String) +(declare-fun z () String) + +(assert (= (str.len x) 1)) +(assert (= (str.++ x y "b" z) "aaaba")) +(check-sat)