P Systems with Active Membranes and Separation Rules

P Sys ems wi h Ac i e Memb anes and Sepa a ion Rules Linqiang PAN1,2, Tse en-Onol ISHDORJ2 1Depa men o Con ol Science and Enginee ing Huazhong Uni e si y o Science and Technology Wuhan 430074, Hubei, People’s Republic o China E-mail: [email p o ec ed] 2Resea ch G oup on Ma hema ical Linguis ics Ro i a i Vi gili Uni e si y Pl. Impe ial T`a aco 1, 43005 Ta agona, Spain E-mail: {lp@ ll, se enonol .ishdo j@es udian s}.u .es Abs ac . The P sys ems a e a class o dis ibu ed pa allel compu ing de ices o a biochemical ype. In his pape , a new de ini ion o sepa a ion ules in P sys ems wi h ac i e memb anes is gi en. Unde he new de ini ion, he e iciency and uni e sali y o P sys ems wi h ac i e memb anes and sepa a ion ules ins ead o di ision a e in es iga ed. 1 In oduc ion The P sys ems a e a class o dis ibu ed pa allel compu ing de ices o a biochemical ype, in oduced in [7], which can be seen as a gene al compu ing a chi ec u e whe e a ious ypes o objec s can be p ocessed by a ious ope a ions. The a ea s a s om he obse a ion ha ce ain p ocesses which ake place in he complex s uc u e o li ing o ganisms can be conside ed as compu a ions. Fo a mo i a ion and de ailed desc ip ion o a ious P sys em models we e e o [7], [9]. In o mally speaking, in P sys ems wi h ac i e memb anes one uses six ypes o ules: (a) mul ise ew i ing ules, (b) ules o in oducing objec s in o memb anes, (c) ules o sending objec s ou o memb anes, (d) ules o dissol ing memb anes, (e) ules o di iding elemen a y memb anes, and ( ) ules o di iding non-elemen a y memb anes. Memb ane di ision – inspi ed om cell di ision well-known in biology – is he mos in es iga ed way o ob aining an exponen ial wo king space in a linea ime, and sol ing on his basis ha d p oblems, ypically NP-comple e p oblems, in polynomial (o en, linea ) ime. De ails can be ound in [8, 9, 10]. Recen ly, also PSPACE-comple e p oblems we e a acked in his way (see [13, 2]). Sepa a ion is also a well known phenomenon o cell biology. Many mac omolecules a e oo la ge o be anspo ed h ough memb anes by means o esicle o ma ion. This p ocess can anspo packages o chemicals ou o he cell. 325 By di ision, he wo new memb anes ha e exac ly he same objec s excep o a mos a pai o di e en objec s; i is also possible ha he wo new memb anes ha e di e en cha ges. Howe e , in he biological phenomenon o sepa a ion, he wo new memb anes e ol ed om a memb ane can ha e much di e ence, such as he numbe o objec s. In [1], sepa a ion ules a e in oduced o P sys ems wi h ac i e memb anes, whe e o each sepa a ion ule, a di e en subse Uo objec s is de ined o ac i a e he memb ane o sepa a e, and by Uobjec s a e pu in o he wo new memb anes. In his pape , we gi e a new de ini ion o sepa a ion ules. In he new de ini ion, o each sepa a ion ule one objec is used o ac i a e sepa a ion; o all sepa a ion ules a uni o m subse O1o objec s is used o deno e which memb ane objec s should go. F om his poin o iew, he new de ini ion is an imp o emen o he de ini ion in [1]. Unde he new de ini ion, he e iciency and uni e sali y o P sys ems wi h ac i e memb anes and sepa a ion ules ins ead o di ision a e in es iga ed. 2 P Sys ems wi h Ac i e Memb anes We assume he eade o be amilia wi h basic elemen s o complexi y heo y and o mal language heo y, o ins ance, om [6, 12, 11], as well as wi h he basic knowledge o memb ane compu ing, o ins ance, om [9] (de ails and ecen esul s om memb ane compu ing can be ound a he web add ess h p://psys ems.disco.unimib.i ). We only men ion ha RE deno e he amily o ecu si ely enume able languages, and ha o a amily o languages FL, by P sF L we deno e he amily o Pa ikh se s o languages in FL; as usual, he Pa ikh mapping associa ed wi h an alphabe Vis deno ed by ΨV. A P sys em wi h ac i e memb anes (and elec ical cha ges) is a cons uc Π = (O, H, µ, w1, . . . , wm, R), whe e: 1. m≥1 ( he ini ial deg ee o he sys em); 2. Ois he alphabe o objec s, whe e O=O1∪O2,O1, O26=∅,O1∩O2=∅; 3. His a ini e se o labels o memb anes; 4. µis a memb ane s uc u e, consis ing o mmemb anes, labeled (no necessa ily in a one- o-one manne ) wi h elemen s o H; 5. w1, . . . , wma e s ings o e O, desc ibing he mul ise s o objec s placed in he m egions o µ; 6. Ris a ini e se o de elopmen al ules, o he ollowing o ms: (a) [ a→ ]e h, o h∈H, e ∈ {+,−,0}, a ∈O, ∈O∗ (objec e olu ion ules, associa ed wi h memb anes and depending on he label and he cha ge o he memb anes, bu no di ec ly in ol ing he memb anes, in he sense ha he memb anes a e nei he aking pa in he applica ion o hese ules no a e hey modi ied by hem); 326 (b)a[ ]e1 h→[b]e2 h, o h∈H, e1, e2∈ {+,−,0}, a, b ∈O (communica ion ules; an objec is in oduced in he memb ane, possibly modi- ied du ing his p ocess; also he pola iza ion o he memb ane can be modi ied, bu no i s label); (c) [ a]e1 h→[ ]e2 hb, o h∈H, e1, e2∈ {+,−,0}, a, b ∈O (communica ion ules; an objec is sen ou o he memb ane, possibly modi ied du ing his p ocess; also he pola iza ion o he memb ane can be modi ied, bu no i s label); (d) [ a]e h→b, o h∈H, e ∈ {+,−,0}, a, b ∈O (dissol ing ules; in eac ion wi h an objec , a memb ane can be dissol ed, while he objec speci ied in he ule can be modi ied); (e) [ a]e1 h→[b]e2 h[c]e3 h, o h∈H, e1, e2, e3∈ {+,−,0}, a, b, c ∈O (di ision ules o elemen a y memb anes; in eac ion wi h an objec , he mem- b ane is di ided in o wo memb anes wi h he same label, possibly o di e en pola iza ions; he objec speci ied in he ule is eplaced in he wo new mem- b anes by possibly new objec s); ( ) [ [ ]α1 h1. . . [ ]α1 hk[ ]α2 hk+1 . . . [ ]α2 hn]α0 h0 →[ [ ]α3 h1. . . [ ]α3 hk]α5 h0[ [ ]α4 hk+1 ...[ ]α4 hn]α6 h0, o k≥1, n > k, hi∈H, 0≤i≤n, and α0, . . . , α6∈ {+,−,0}wi h {α1, α2}={+,−}; i he memb ane wi h he label h0con ains o he mem- b anes han hose wi h he labels h1, . . . , hnspeci ied abo e, hen hey mus ha e neu al cha ges in o de o make his ule applicable; hese memb anes a e duplica ed and hen a e pa o he con en s o bo h new copies o he mem- b ane h0 (di ision o non-elemen a y memb anes; his is possible only i a memb ane con ains wo immedia ely lowe memb anes o opposi e pola iza ion, + and −; he memb anes o opposi e pola iza ions a e sepa a ed in he wo new mem- b anes, bu hei pola iza ion can change; always, all memb anes o opposi e pola iza ions a e sepa a ed by applying his ule). (No e ha , in o de o simpli y he w i ing, in con as o he s yle cus oma y in he li e a u e, we ha e omi ed he label o he le pa en hesis om a pai o pa en heses which iden i ies a memb ane.) The ules o ype (a) a e applied in he pa allel way (all objec s which can e ol e by such a ule should do i ), while he ules o ypes (b),(c),(d),(e),( ) a e used sequen ially, in he sense ha one memb ane can be used by a mos one ule o hese ypes a a ime. In o al, he ules a e used in he non-de e minis ic maximally pa allel manne : all objec s and all memb anes which can e ol e, should e ol e. Only hal ing compu a ions gi e a esul , non-hal ing compu a ions gi e no ou pu . The sepa a ion ules in oduced in [1] a e o he ollowing o m (wi hou pola iza ions): (h0) [ O]h→[U]h[O−U]h, o h∈H, U ⊂O. I pola iza ion is conside ed, hey will be o he o m: (h) [ O]e1 h→[U]e2 h[O−U]e3 h, o h∈H, U ⊂O. 327 He e, we in oduce a new de ini ion o sepa a ion ules. (g) [ a]e1 h→[O1]e2 h[O2]e3 h, o h∈H,e1, e2, e3∈ {+,−,0},a∈O (sepa a ion ules o elemen a y memb anes; in eac ion wi h an objec , he memb ane is sepa a ed in o wo memb anes wi h he same label, possibly di - e en pola iza ion; a he same ime, he objec acan e ol e; he objec s om O1a e placed in he i s memb ane, hose om O2a e placed in he second memb ane). As he ules o ypes (b),(c),(d),(e), and ( ), he ules o ype (g) a e used sequen ially, in he sense ha one memb ane can be used by a mos one ule o hese ypes a a ime. I a he same ime a memb ane his sepa a ed, and he e a e objec s in his memb ane which e ol e by means o ules o ype (a), hen in he wo new memb anes we in oduce he esul o e olu ion; ha is, we suppose ha i s he e olu ion ules o ype (a) a e used, changing he objec s, hen sepa a ion is p oduced. O cou se, his p ocess akes one s ep. No e he di e ence be ween di ision ule and sepa a ion ule. In di ision ule, excep o he objec speci ied in he ule is eplaced by wo possibly di e en new objec s, he wo new memb anes ha e he same copy o objec s. Bu in sepa a ion ule, he new objec s a e placed in o he wo new memb anes acco ding o O1and O2, hese wo new memb anes can ha e much di e ence, such as he numbe o objec s. Fo he di e ence be ween he de ini ions o (g) and (h), see he in oduc ion. To unde s and wha i means sol ing a p oblem in a uni o m and con luen way, he e we b ie ly ecall some ela ed no ions. Gi en a decision p oblem X, we say ha i can be sol ed in polynomial (linea ) ime by ecognizing P sys ems in a uni o m way, i , in o mally speaking, we can cons uc in polynomial ime a amily o ecognizing P sys ems Πn,n∈N, associa ed wi h he sizes no ins ances X(n) o he p oblem, such ha he sys em will always s op in a polynomial (linea , espec i ely) numbe o s eps, sending ou he objec yes i he ins ance X(n) has a posi i e answe and he objec no i he ins ance X(n) has a nega i e answe . I he compu a ion o a P sys em is nonde e minis ic, bu all b anches o a compu a ion e en ually each a unique con igu a ion, hen we say ha he sys em is con luen . In he nex sec ion, we will show ha P sys ems wi h sepa a ion ules ins ead o di ision ules can sol e he SAT p oblem in linea ime in a uni o m and de e minis ic way. 3 Sol ing SAT by P Sys ems wi h Sepa a ion Rules Theo em 3.1 P sys ems wi h ules o ypes (a),(b),(c), and (g)can sol e SAT in linea ime in a uni o m and de e minis ic way. P oo . Le us conside a p oposi ional o mula in he conjunc i e no mal o m: β=C1∧ · · · ∧ Cm, Ci=yi,1∨ · · · ∨ yi,li,1≤i≤m, whe e yi,k ∈ {xj,¬xj|1≤j≤n},1≤i≤m, 1≤k≤li. The ins ance β( o which he size (m, n) is associa ed) is encoded as a mul ise o e V(hn, mi) = {xi,j,¯xi,j |1≤i≤m, 1≤j≤n}. 328 The objec xi,j ep esen s he a iable xjappea ing in he clause Ciwi hou nega ion, and objec ¯xi,j ep esen s he a iable xjappea ing in he clause Ciwi h nega ion. Thus, he inpu mul ise is w={xi,j |xj∈ {yi,k |1≤k≤li},1≤i≤m, 1≤j≤n} ∪ {¯xi,j | ¬xj∈ {yi,k |1≤k≤li},1≤i≤m, 1≤j≤n}. Fo gi en (n, m)∈N2, we cons uc a ecognizing P sys em (Π(hn, mi), V (hn, mi),2) wi h: Π(hn, mi)=(O(hn, mi), H, µ, w1, w2, R), O(hn, mi) = O1∪O2, O1={xi,j,¯xi,j,|0≤i≤m, 1≤j≤n} ∪ {ci|1≤i≤m+ 2} ∪ {di|1≤i≤2n+ 2m+ 2}∪{ i,j |0≤i≤m, 1≤j≤n} ∪ {e, , λ, yes,no}, O2={x0 i,j,¯x0 i,j,|0≤i≤m, 1≤j≤n} ∪ {d0 i|1≤i≤n} ∪ { i,j |0≤i≤m, 1≤j≤n}∪{e0}, µ= [ [ ]2]1, w1=λ, w2=d1, H={1,2}, and he ollowing ules (we also gi e explana ions abou he use o hese ules): 1. [ di]0 2→[O1]+ 2[O2]− 2, 1 ≤i≤n. In memb ane wi h label 2, when i is “elec ically neu al”, objec dicauses he memb ane o sepa a e and o choose o a a iable xi, 1 ≤i≤n, bo h alues ue and alse, in o m o cha ges + and −o he wo c ea ed memb anes wi h he label 2. These ules allow us o ha e 2nin e nal memb anes, in ns eps. 2. [ xi,j →xi,jx0 i,j]0 2, 1 ≤i≤m, 1 ≤j≤n. [ ¯xi,j →¯xi,j ¯x0 i,j]0 2, 1 ≤i≤m, 1 ≤j≤n. [di→di+1ed0 i+1e0]0 2, 1 ≤i≤n−1. A he same ime wi h using he ule o ype (1), he objec s e ol e by ules o ype (2). 3. [ xi,1→ i,1]+ 2, 1 ≤i≤m. [ ¯xi,1→λ]+ 2, 1 ≤i≤m. [x0 i,1→λ]− 2, 1 ≤i≤m. [ ¯x0 i,1→ 0 i,1]− 2, 1 ≤i≤m. The ules o ype (3) y o implemen a p ocess allowing he in e nal memb anes o encode he assignmen o a a iable and, simul aneously, o check he alue o all clauses by his assignmen , in such a way ha , i he clause is ue, hen an objec i,1o 0 i,1will appea in he memb ane. In o he case, he objec encoding he a iable will disappea . 4. [ xi,j →xi,j−1]+ 2, 1 ≤i≤m, 2 ≤j≤n. [ ¯xi,j →¯xi,j−1]+ 2, 1 ≤i≤m, 2 ≤j≤n. [x0 i,j →xi,j−1]− 2, 1 ≤i≤m, 2 ≤j≤n. 329 [ ¯x0 i,j →¯xi,j−1]− 2, 1 ≤i≤m, 2 ≤j≤n. The check p ocess desc ibed in he ules o ype (3) is always made wi h espec o he i s a iable appea ing in he in e nal memb ane. Hence, he ules o ype (4) ake cha ge o making a cyclic pa h h ough all he a iables o ge ha , ini ially, he i s a iable is x1, hen x2, and so on. 5. [ e]+ 1→[ ]0 1e. [e0]− 1→[ ]0 1e. [d0 i→di]− 2, 1 ≤i≤n. The auxilia y objec s eand e0exi he memb ane changing he pola iza ions o neu al and he objec d0 iin he memb ane wi h nega i e cha ge e ol es o he objec di( o he use o he ules o ype (1) and he hi d ules o ype (2)), so ha he abo e desc ibed gene a ing p ocess o he assignmen s and he encoding o he sa is ied clauses can cycle. 6. [ i,k → i,k+1 0 i,k+1]0 2, o 1 ≤i≤m, 1 ≤k≤n−1. [ 0 i,k → i,k+1 0 i,k+1]0 2, o 1 ≤i≤m, 1 ≤k≤n−1. These ules a e designed o deno e he ac : i clause Ciis sa is ied by he assignmen encoded by a memb ane, hen he new memb anes ob ained om i by sepa a ion also sa is y he clause Ci. The second subsc ip o i,k o 0 i,k is used o synch o- niza ion, which is necessa y, because o he use o objec s i,n and 0 i,n in he ules o ypes (11), (12), and (13). 7. [ di→di+1]0 2, o n≤i≤2n−2. [d2n−2→d2n−1c1]0 2. Th ough he coun e objec s di, he ules o ype (7) con ol he p ocess o synch o- niza ion o he objec s i,k and 0 i,k in he in e nal memb anes. 8. [ d2n−1]0 2→[ ]+ 2d2n−1. The applica ion o he ules o ype (8) will show ha he sys em is eady o check which clauses a e ue by he assignmen encoded by an in e nal memb ane. 9. [ di→di+1]0 1, 2n−1≤i≤2n+ 2m+ 1. The ules o ype (9) supply coun e objec s diin he skin, in such a way ha , i objec s d2n+2m−1appea , hen hey show he end o he checking o he clauses. The objec s di, wi h 2n+ 2m≤i≤2n+ 2m+ 2, will con ol he inal s age o he compu a ion. 10. [ 1,n]+ 2→[ ]− 2 1,n. [ 0 1,n]+ 2→[ ]− 2 1,n. Fo all 2nin e nal memb anes, we check whe he 1,n o 0 1,n is p esen in each memb ane. I his is he case, hen 1,n o 0 1,n is sen ou o he memb ane whe e i is p esen (one copy o 1,n o 0 1,n exi s he memb ane whe e i is p esen , he o he copies will e ol e o 0,n o 0 0,n by he ules o ype (10), which will ne e e ol e again), changing in his way he pola iza ion o ha memb ane, o nega i e. The memb anes which do no con ain he objec 1,n o 0 1,n emain posi i e and hey will no longe e ol e, as no u he ule can be applied o hem. 11. [ i,n → i−1,n]− 2, o 1 ≤i≤n. [ 0 i,n → 0 i−1,n]− 2, o 1 ≤i≤n. 330 The ules o ype (10) always wo k wi h espec o he objec s 1,n o 0 1,n, The elabel in he ules o ype (11) akes cha ge o making a cyclic pa h h ough all i,n and 0 i,n, and e ol es he objec s 1,n o 0 1,n o 0,n o 0 0,n (which will ne e e ol e again). 12. 1,n[ ]− 2→[ 0,n]+ 2. The objec s 1,n om he skin memb ane e u n o in e nal memb anes wi h nega i e cha ge, changing o 0,n, and e u ning he pola iza ion o he memb ane o posi i e. This makes possible he use o ules o ype (10). No e ha in he skin memb ane he numbe o copies o 1,n is equal o he numbe o memb anes wi h nega i e cha ge; hus, because o pa allelism, each memb ane which p e iously con ained objec s 1,n o 0 1,n will now con ain an objec 0,n. 13. [ ci→ci+1]− 2, 1 ≤i≤m. The p esence o objec ci(wi h 2 ≤i≤m+ 1) in he in e nal memb ane shows ha he assignmen makes he i s i−1 clauses ue. 14. [ cm+1]+ 2→[ ]+ 2cm+1. The p esence o he objec cm+1 shows ha all clauses a e sa is ied by he assignmen encoded by an in e nal memb ane. The ule o ype (14) sends o he skin he objec s cm+1 appea ing in he in e nal memb anes. 15. [ cm+1 →cm+2 ]0 1. The objec s cm+1 in he skin e ol e o objec s cm+2 . The objec s in he skin a e p oduced simul aneously wi h he appea ance o he objec s d2n+2m+1 in he skin, and hey will be used o ou pu he compu ing esul . 16. [ ]0 1→[ ]+ 1 . The ule o ype (16) sends ou o he sys em an objec changing he pola iza ion o he skin o posi i e, hen objec s emaining in he skin a e no able o e ol e. Then by ule o ype (17), he objec cm+2 can exi he skin p oducing an objec yes, elling us ha he o mula is sa is iable, and he compu a ion hal s. 17. [ cm+2]+ 1→[ ]− 1yes. The applica ion o he ule o ype (17) changes he pola iza ion in he skin mem- b ane o nega i e in o de ha he objec s cm+2 emaining in i a e no able o con inue e ol ing. 18. [ d2n+2m+2]0 1→[ ]+ 1no. By he ule (18) he objec d2n+2m+2 only e ol es when he skin has neu al cha ge ( his is he case when he o mula is no sa is iable). Then he sys em will e ol e sending ou o he en i onmen an objec no and changing he pola iza ion o he skin o posi i e, in o de ha objec s d2n+2m+2 emaining in he skin, do no e ol e. F om he p e ious explana ion o he use o ules, one can easily see how his P sys em wo ks. I is clea ha he objec yes is sen o he en i onmen i and only i he o mula βis sa is iable. This is achie ed in 3n+ 2m+ 4 s eps: in 2ns eps we c ea e 2nin e nal memb anes (as well as he 2ndi e en u h-assignmen s), hen ns eps o synch oniza ion; i akes 2ms eps o check whe he all clauses a e sa is ied by an assignmen ; u he 4 s eps a e necessa y o ou pu he compu ing esul yes. I o mula 331 βis no sa is iable, hen a s ep 3n+ 2m+ 4 he sys em sends he objec no o he en i onmen . The e o e, he amily o memb ane sys ems we ha e cons uc ed is sound, con luen , and linea ly e icien . To p o e ha he amily is uni o m, we ha e o show ha o a gi en size, he con- s uc ion o P sys ems desc ibed in he p oo can be done in polynomial ime by a Tu ing machine. We omi he de ailed cons uc ion due o he ac ha i is s aigh o wa d bu cumbe some as explained in he p oo o Theo em 7.2.3 in [9] (al hough P sys ems in [9] a e semi-uni o m). So SAT p oblem was decided in linea ime (3n+2m+2) by ecognizing ac i e P sys ems wi h sepa a ion ule in a uni o m way, and his concludes he p oo . 2 4 Remo ing Pola iza ions Following he idea in [3, 4], le us conside now ules o ypes (a)−(e) and (g) wi hou pola iza ions. They a e o he ollowing o ms (because “no pola iza ion” means “neu al pola iza ion”, we add he subsc ip 0 o he p e ious le e s iden i ying he six ypes o ules; as abo e, O=O1∪O2is he alphabe o objec s and His he se o labels o memb anes): (a0) [ a→ ]h, whe e a∈O, ∈O∗, and h∈H, (b0)a[ ]h→[b]h, whe e a, b ∈Oand h∈H, (c0) [ a]h→[ ]hb, whe e a, b ∈Oand h∈H, (d0) [ a]h→b, whe e a, b ∈Oand h∈H, (e0) [ a]h→[b]h[c]h, whe e a, b, c ∈Oand h∈H, (g0) [ a]h→[O1]h[O2]h, o h∈H,a∈O. Rules o ypes (b),(c),(e),(g) in Sec ion 2 we e in oduced wi hou he capabili y o changing he label o memb anes hey in ol e ( his makes no sense o dissol ing ules), bu in [9] one al eady conside s ules o ype (e) which can change bo h he label and he pola iza ion o memb anes. Such ules a e o he o m [a]e1 h1→[b]e2 h2[c]e3 h3,wi h a, b, c ∈O, e1, e2, e3∈ {+,−,0},and h1, h2, h3∈H, and hey ha e been called o ype (e0). We ex end his idea and his no a ion o ules o ypes (b0), (c0), (e0), (g0): hei p imed e sions indica e he ac ha he labels can be changed. Speci ically, hese ules a e o he ollowing o ms: (b0 0)a[ ]h1→[b]h2, whe e a, b ∈Oand h1, h2∈H, (c0 0) [ a]h1→[ ]h2b, whe e a, b ∈Oand h1, h2∈H, (e0 0) [ a]h1→[b]h2[c]h3, whe e a, b, c ∈Oand h1, h2, h3∈H, (g0 0) [ a]h1→[O1]h2[O2]h3, o h1, h2, h3∈H,a∈O. In he ollowing, we conside he e iciency and uni e sali y o ac i e P sys ems wi hou pola iza ion wi h sepa a ion ules ins ead o di ision. 332 4.1 E iciency Theo em 4.1 P sys ems wi h ules o ypes (a0),(b0),(c0),(g0 0)can sol e SAT in linea ime in a uni o m and con luen way. P oo . Le us conside a p oposi ional o mula in he conjunc i e no mal o m: β=C1∧ · · · ∧ Cm, Ci=yi,1∨ · · · ∨ yi,li,1≤i≤m, whe e yi,k ∈ {xj,¬xj|1≤j≤n},1≤i≤m, 1≤k≤li. The ins ance β( o which he size (m, n) is associa ed) is encoded as a mul ise o e V(hn, mi) = {xi,j,¯xi,j |1≤i≤m, 1≤j≤n}. The objec xi,j ep esen s he a iable xjappea ing in he clause Ciwi hou nega ion, and objec ¯xi,j ep esen s he a iable xjappea ing in he clause Ciwi h nega ion. Thus, he inpu mul ise is w={xi,j |xj∈ {yi,k |1≤k≤li},1≤i≤m, 1≤j≤n} ∪ {¯xi,j | ¬xj∈ {yi,k |1≤k≤li},1≤i≤m, 1≤j≤n}. Fo gi en (n, m)∈N2, we cons uc a ecognizing P sys em (Π(hn, mi), V (hn, mi),2) wi h: Π(hn, mi)=(O(hn, mi), H, µ, w1, w2, w7, R), O(hn, mi) = O1∪O2, O1={xi,j,¯xi,j |1≤i≤m, 0≤j≤n}∪{di|0≤i≤2n+ 2m+ 6} ∪ {ci|1≤i≤m} ∪ {λ, e, 0, 1,yes,no}, O2={x0 i,j,¯x0 i,j |1≤i≤m, 0≤j≤n}∪{d0 i|0≤i≤n−1} ∪ {c0 i|1≤i≤m}, µ= [ [ ]2[ ]7]1, w1=λ, w2=w7=d0, H={0,1,2,3,4,5,6,7}, and he ollowing ules (we also gi e explana ions abou he use o hese ules): Gene a ion phase G1 [ di]2→[O1]3[O2]4, 0 ≤i < n. [di→did0 i]2, 0 ≤i < n. G2 [ di]3→[O1]2[O2]0, 0 ≤i < n. [di→di+1d0 0]3, 0 ≤i < n. G3 [ d0 i]4→[O1]2[O2]0, 0 ≤i < n. [d0 i→di+1d0 0]4, 0 ≤i < n. G4 [ dn]2→[O1]5[O2]0. [dn→d0d0 0]2. 333 8. [ A→#] , o all A∈N2. 9. [ # →#]h, o all h∈H. 10. [ a] →[ ] a. 11. [ a]1→[ ]1a, o all a∈T. The equali y ΨT(L(G)) = Ps(Π) easily ollows om he abo e explana ions. 2 Rema k 4.1 In he abo e p oo , he ules o ype (c0)a e only used o sending he esul o a compu a ion ou o he sys em. The e o e, ules o ypes (a0)and (g0 0)a e su icien o each uni e sali y o memb ane sys ems wi h in e nal ou pu . 5 Final Rema k In his pape , sepa a ion is in oduced in o ac i e P sys ems, and he e iciency and uni- e sali y o ac i e P sys ems wi h sepa a ion ules ins ead o di ision a e in es iga ed. The uni e sali y esul is ob ained by a di ec p oo . I s ill emains open using P sys ems wi h sepa a ion ules o simula e P sys ems wi h di ision ules. Acknowledgemen s. The au ho s acknowledge IST-2001-32008 p ojec “MolCoNe ”. The i s au ho (he is also he co esponding au ho ) is also suppo ed by g an DGU- SB2001-0092 om Spanish Minis y o Educa ion, Cul u e, and Spo , Na ional Na u al Science Founda ion o China (G an No. 60373089), and Huazhong Uni e si y o Science and Technology Founda ion. The second au ho acknowledges The S a e T aining Fund o he Minis y o Science, Technology, Educa ion and Cul u e o Mongolia. Re e ences [1] A. Alhazo , T.-O. Ishdo j, Memb ane Ope a ions in P Sys ems wi h Ac i e Mem- b anes, Manusc ip ci cula ed du ing he Second B ains o ming Week on Memb ane Compu ing, Se illa, Spain, Feb. 2-7, 2004. [2] A. Alhazo , C. Ma ´ın-Vide, L. Pan, Sol ing a PSPACE-Comple e P oblem by P Sys ems wi h Res ic ed Ac i e Memb anes, Fundamen a In o ma icae, 58, 2 (2003), 66–77. [3] A. Alhazo , L. Pan, Pola iza ionless P Sys ems wi h Ac i e Memb anes, G amma s, 7, 1 (2004). [4] A. Alhazo , L. Pan, Gh. P˘aun, T ading Pola iza ions o Labels in P Sys ems wi h Ac i e Memb anes, submi ed 2003. [5] J. 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