YES We show the termination of the TRS R: app(app(.(),|1|()),x) -> x app(app(.(),x),|1|()) -> x app(app(.(),app(i(),x)),x) -> |1|() app(app(.(),x),app(i(),x)) -> |1|() app(app(.(),app(i(),y)),app(app(.(),y),z)) -> z app(app(.(),y),app(app(.(),app(i(),y)),z)) -> z app(i(),|1|()) -> |1|() app(i(),app(i(),x)) -> x app(app(map(),f),nil()) -> nil() app(app(map(),f),app(app(cons(),x),xs)) -> app(app(cons(),app(f,x)),app(app(map(),f),xs)) app(app(filter(),f),nil()) -> nil() app(app(filter(),f),app(app(cons(),x),xs)) -> app(app(app(app(filter2(),app(f,x)),f),x),xs) app(app(app(app(filter2(),true()),f),x),xs) -> app(app(cons(),x),app(app(filter(),f),xs)) app(app(app(app(filter2(),false()),f),x),xs) -> app(app(filter(),f),xs) Instead we prove termination of the uncurried system: app(._0(),y) -> ._1(y) app(._1(x1),y) -> ._2(x1,y) app(cons_0(),y) -> cons_1(y) app(cons_1(x1),y) -> cons_2(x1,y) app(filter_0(),y) -> filter_1(y) app(filter_1(x1),y) -> filter_2(x1,y) app(filter2_0(),y) -> filter2_1(y) app(filter2_1(x1),y) -> filter2_2(x1,y) app(filter2_2(x1,x2),y) -> filter2_3(x1,x2,y) app(filter2_3(x1,x2,x3),y) -> filter2_4(x1,x2,x3,y) app(i_0(),y) -> i_1(y) app(map_0(),y) -> map_1(y) app(map_1(x1),y) -> map_2(x1,y) ._2(|1|_0(),x) -> x ._2(x,|1|_0()) -> x ._2(i_1(x),x) -> |1|_0() ._2(x,i_1(x)) -> |1|_0() ._2(i_1(y),._2(y,z)) -> z ._2(y,._2(i_1(y),z)) -> z i_1(|1|_0()) -> |1|_0() i_1(i_1(x)) -> x map_2(f,nil_0()) -> nil_0() map_2(f,cons_2(x,xs)) -> cons_2(app(f,x),map_2(f,xs)) filter_2(f,nil_0()) -> nil_0() filter_2(f,cons_2(x,xs)) -> filter2_4(app(f,x),f,x,xs) filter2_4(true_0(),f,x,xs) -> cons_2(x,filter_2(f,xs)) filter2_4(false_0(),f,x,xs) -> filter_2(f,xs) -- SCC decomposition. Consider the dependency pair problem (P, R), where P consists of p1: app#(._1(x1),y) -> ._2#(x1,y) p2: app#(filter_1(x1),y) -> filter_2#(x1,y) p3: app#(filter2_3(x1,x2,x3),y) -> filter2_4#(x1,x2,x3,y) p4: app#(i_0(),y) -> i_1#(y) p5: app#(map_1(x1),y) -> map_2#(x1,y) p6: map_2#(f,cons_2(x,xs)) -> app#(f,x) p7: map_2#(f,cons_2(x,xs)) -> map_2#(f,xs) p8: filter_2#(f,cons_2(x,xs)) -> filter2_4#(app(f,x),f,x,xs) p9: filter_2#(f,cons_2(x,xs)) -> app#(f,x) p10: filter2_4#(true_0(),f,x,xs) -> filter_2#(f,xs) p11: filter2_4#(false_0(),f,x,xs) -> filter_2#(f,xs) and R consists of: r1: app(._0(),y) -> ._1(y) r2: app(._1(x1),y) -> ._2(x1,y) r3: app(cons_0(),y) -> cons_1(y) r4: app(cons_1(x1),y) -> cons_2(x1,y) r5: app(filter_0(),y) -> filter_1(y) r6: app(filter_1(x1),y) -> filter_2(x1,y) r7: app(filter2_0(),y) -> filter2_1(y) r8: app(filter2_1(x1),y) -> filter2_2(x1,y) r9: app(filter2_2(x1,x2),y) -> filter2_3(x1,x2,y) r10: app(filter2_3(x1,x2,x3),y) -> filter2_4(x1,x2,x3,y) r11: app(i_0(),y) -> i_1(y) r12: app(map_0(),y) -> map_1(y) r13: app(map_1(x1),y) -> map_2(x1,y) r14: ._2(|1|_0(),x) -> x r15: ._2(x,|1|_0()) -> x r16: ._2(i_1(x),x) -> |1|_0() r17: ._2(x,i_1(x)) -> |1|_0() r18: ._2(i_1(y),._2(y,z)) -> z r19: ._2(y,._2(i_1(y),z)) -> z r20: i_1(|1|_0()) -> |1|_0() r21: i_1(i_1(x)) -> x r22: map_2(f,nil_0()) -> nil_0() r23: map_2(f,cons_2(x,xs)) -> cons_2(app(f,x),map_2(f,xs)) r24: filter_2(f,nil_0()) -> nil_0() r25: filter_2(f,cons_2(x,xs)) -> filter2_4(app(f,x),f,x,xs) r26: filter2_4(true_0(),f,x,xs) -> cons_2(x,filter_2(f,xs)) r27: filter2_4(false_0(),f,x,xs) -> filter_2(f,xs) The estimated dependency graph contains the following SCCs: {p2, p3, p5, p6, p7, p8, p9, p10, p11} -- Reduction pair. Consider the dependency pair problem (P, R), where P consists of p1: app#(filter_1(x1),y) -> filter_2#(x1,y) p2: filter_2#(f,cons_2(x,xs)) -> app#(f,x) p3: app#(map_1(x1),y) -> map_2#(x1,y) p4: map_2#(f,cons_2(x,xs)) -> map_2#(f,xs) p5: map_2#(f,cons_2(x,xs)) -> app#(f,x) p6: app#(filter2_3(x1,x2,x3),y) -> filter2_4#(x1,x2,x3,y) p7: filter2_4#(false_0(),f,x,xs) -> filter_2#(f,xs) p8: filter_2#(f,cons_2(x,xs)) -> filter2_4#(app(f,x),f,x,xs) p9: filter2_4#(true_0(),f,x,xs) -> filter_2#(f,xs) and R consists of: r1: app(._0(),y) -> ._1(y) r2: app(._1(x1),y) -> ._2(x1,y) r3: app(cons_0(),y) -> cons_1(y) r4: app(cons_1(x1),y) -> cons_2(x1,y) r5: app(filter_0(),y) -> filter_1(y) r6: app(filter_1(x1),y) -> filter_2(x1,y) r7: app(filter2_0(),y) -> filter2_1(y) r8: app(filter2_1(x1),y) -> filter2_2(x1,y) r9: app(filter2_2(x1,x2),y) -> filter2_3(x1,x2,y) r10: app(filter2_3(x1,x2,x3),y) -> filter2_4(x1,x2,x3,y) r11: app(i_0(),y) -> i_1(y) r12: app(map_0(),y) -> map_1(y) r13: app(map_1(x1),y) -> map_2(x1,y) r14: ._2(|1|_0(),x) -> x r15: ._2(x,|1|_0()) -> x r16: ._2(i_1(x),x) -> |1|_0() r17: ._2(x,i_1(x)) -> |1|_0() r18: ._2(i_1(y),._2(y,z)) -> z r19: ._2(y,._2(i_1(y),z)) -> z r20: i_1(|1|_0()) -> |1|_0() r21: i_1(i_1(x)) -> x r22: map_2(f,nil_0()) -> nil_0() r23: map_2(f,cons_2(x,xs)) -> cons_2(app(f,x),map_2(f,xs)) r24: filter_2(f,nil_0()) -> nil_0() r25: filter_2(f,cons_2(x,xs)) -> filter2_4(app(f,x),f,x,xs) r26: filter2_4(true_0(),f,x,xs) -> cons_2(x,filter_2(f,xs)) r27: filter2_4(false_0(),f,x,xs) -> filter_2(f,xs) The set of usable rules consists of r1, r2, r3, r4, r5, r6, r7, r8, r9, r10, r11, r12, r13, r14, r15, r16, r17, r18, r19, r20, r21, r22, r23, r24, r25, r26, r27 Take the reduction pair: generalized weighted path order (>=MG, >G) base order 1: matrix interpretation with standard point-wise order: carrier: N^1 order: standard order interpretations: app#_A(x1,x2) = x1 filter_1_A(x1) = x1 + 7 filter_2#_A(x1,x2) = x1 + 6 cons_2_A(x1,x2) = 1 map_1_A(x1) = x1 + 3 map_2#_A(x1,x2) = x1 + 2 filter2_3_A(x1,x2,x3) = x1 + x2 + x3 + 7 filter2_4#_A(x1,x2,x3,x4) = x2 + 6 false_0_A() = 5 app_A(x1,x2) = x1 + x2 + 3 true_0_A() = 2 ._0_A() = 1 ._1_A(x1) = x1 + 2 ._2_A(x1,x2) = x1 + x2 + 3 cons_0_A() = 3 cons_1_A(x1) = 2 filter_0_A() = 5 filter_2_A(x1,x2) = 4 filter2_0_A() = 1 filter2_1_A(x1) = x1 + 3 filter2_2_A(x1,x2) = x1 + x2 + 5 filter2_4_A(x1,x2,x3,x4) = 4 i_0_A() = 1 i_1_A(x1) = x1 + 2 map_0_A() = 1 map_2_A(x1,x2) = 2 |1|_0_A() = 1 nil_0_A() = 1 base order 2: marked-algebra reduction triple (>=A, >=A!, >A!): max/plus interpretation on natural numbers: app#_A(x1,x2) = max{15, x1 - 58, x2 + 1} filter_1_A(x1) = x1 + 37 filter_2#_A(x1,x2) = max{15, x1 - 28, x2 - 12} cons_2_A(x1,x2) = max{x1 + 13, x2} map_1_A(x1) = x1 + 31 map_2#_A(x1,x2) = max{15, x1 - 27, x2 + 1} filter2_3_A(x1,x2,x3) = max{x1 - 57, x2 + 30, x3 + 57} filter2_4#_A(x1,x2,x3,x4) = max{15, x1 - 115, x2 - 28, x3 - 1, x4 - 12} false_0_A = 118 app_A(x1,x2) = max{x1 - 44, x2 + 109} true_0_A = 114 ._0_A = 35 ._1_A(x1) = x1 + 45 ._2_A(x1,x2) = max{109, x1 + 1, x2 + 1} cons_0_A = 31 cons_1_A(x1) = x1 + 57 filter_0_A = 31 filter_2_A(x1,x2) = max{15, x1 - 14, x2 + 1} filter2_0_A = 31 filter2_1_A(x1) = x1 + 31 filter2_2_A(x1,x2) = max{x1 - 13, x2 + 74} filter2_4_A(x1,x2,x3,x4) = max{15, x1 - 119, x2 - 14, x3 + 13, x4 + 1} i_0_A = 31 i_1_A(x1) = max{107, x1} map_0_A = 31 map_2_A(x1,x2) = max{x1 - 13, x2 + 109} |1|_0_A = 109 nil_0_A = 16 app#!_A(x1,x2) = max{3, x1 - 58, x2 - 142} filter_1!_A(x1) = 0 filter_2#!_A(x1,x2) = 0 cons_2!_A(x1,x2) = max{2, x1 - 124, x2 - 141} map_1!_A(x1) = max{2, x1 - 34} map_2#!_A(x1,x2) = max{0, x2 - 142} filter2_3!_A(x1,x2,x3) = max{0, x1 - 114, x2 - 157, x3 - 126} filter2_4#!_A(x1,x2,x3,x4) = 0 false_0!_A = 0 app!_A(x1,x2) = max{4, x1 - 32, x2 - 3} true_0!_A = 6 ._0!_A = 1 ._1!_A(x1) = max{2, x1 - 107} ._2!_A(x1,x2) = max{13, x1 - 108, x2 - 108} cons_0!_A = 2 cons_1!_A(x1) = 1 filter_0!_A = 0 filter_2!_A(x1,x2) = max{5, x1 - 156, x2 - 17} filter2_0!_A = 1 filter2_1!_A(x1) = max{2, x1 - 116} filter2_2!_A(x1,x2) = max{4, x1 - 115, x2 - 158} filter2_4!_A(x1,x2,x3,x4) = max{1, x1 - 113, x2 - 156, x3 - 125, x4 - 17} i_0!_A = 1 i_1!_A(x1) = max{2, x1 - 110} map_0!_A = 1 map_2!_A(x1,x2) = max{3, x1 - 33, x2 - 17} |1|_0!_A = 0 nil_0!_A = 0 partial status: pi(app#) = [1] pi(filter_1) = [1] pi(filter_2#) = [] pi(cons_2) = [] pi(map_1) = [1] pi(map_2#) = [] pi(filter2_3) = [3] pi(filter2_4#) = [] pi(false_0) = [] pi(app) = [1, 2] pi(true_0) = [] pi(._0) = [] pi(._1) = [1] pi(._2) = [1, 2] pi(cons_0) = [] pi(cons_1) = [] pi(filter_0) = [] pi(filter_2) = [] pi(filter2_0) = [] pi(filter2_1) = [1] pi(filter2_2) = [1, 2] pi(filter2_4) = [] pi(i_0) = [] pi(i_1) = [] pi(map_0) = [] pi(map_2) = [] pi(|1|_0) = [] pi(nil_0) = [] The following rules are removed: p1, p2, p3, p5, p6 -- SCC decomposition. Consider the dependency pair problem (P, R), where P consists of p1: map_2#(f,cons_2(x,xs)) -> map_2#(f,xs) p2: filter2_4#(false_0(),f,x,xs) -> filter_2#(f,xs) p3: filter_2#(f,cons_2(x,xs)) -> filter2_4#(app(f,x),f,x,xs) p4: filter2_4#(true_0(),f,x,xs) -> filter_2#(f,xs) and R consists of: r1: app(._0(),y) -> ._1(y) r2: app(._1(x1),y) -> ._2(x1,y) r3: app(cons_0(),y) -> cons_1(y) r4: app(cons_1(x1),y) -> cons_2(x1,y) r5: app(filter_0(),y) -> filter_1(y) r6: app(filter_1(x1),y) -> filter_2(x1,y) r7: app(filter2_0(),y) -> filter2_1(y) r8: app(filter2_1(x1),y) -> filter2_2(x1,y) r9: app(filter2_2(x1,x2),y) -> filter2_3(x1,x2,y) r10: app(filter2_3(x1,x2,x3),y) -> filter2_4(x1,x2,x3,y) r11: app(i_0(),y) -> i_1(y) r12: app(map_0(),y) -> map_1(y) r13: app(map_1(x1),y) -> map_2(x1,y) r14: ._2(|1|_0(),x) -> x r15: ._2(x,|1|_0()) -> x r16: ._2(i_1(x),x) -> |1|_0() r17: ._2(x,i_1(x)) -> |1|_0() r18: ._2(i_1(y),._2(y,z)) -> z r19: ._2(y,._2(i_1(y),z)) -> z r20: i_1(|1|_0()) -> |1|_0() r21: i_1(i_1(x)) -> x r22: map_2(f,nil_0()) -> nil_0() r23: map_2(f,cons_2(x,xs)) -> cons_2(app(f,x),map_2(f,xs)) r24: filter_2(f,nil_0()) -> nil_0() r25: filter_2(f,cons_2(x,xs)) -> filter2_4(app(f,x),f,x,xs) r26: filter2_4(true_0(),f,x,xs) -> cons_2(x,filter_2(f,xs)) r27: filter2_4(false_0(),f,x,xs) -> filter_2(f,xs) The estimated dependency graph contains the following SCCs: {p1} {p2, p3, p4} -- Reduction pair. Consider the dependency pair problem (P, R), where P consists of p1: map_2#(f,cons_2(x,xs)) -> map_2#(f,xs) and R consists of: r1: app(._0(),y) -> ._1(y) r2: app(._1(x1),y) -> ._2(x1,y) r3: app(cons_0(),y) -> cons_1(y) r4: app(cons_1(x1),y) -> cons_2(x1,y) r5: app(filter_0(),y) -> filter_1(y) r6: app(filter_1(x1),y) -> filter_2(x1,y) r7: app(filter2_0(),y) -> filter2_1(y) r8: app(filter2_1(x1),y) -> filter2_2(x1,y) r9: app(filter2_2(x1,x2),y) -> filter2_3(x1,x2,y) r10: app(filter2_3(x1,x2,x3),y) -> filter2_4(x1,x2,x3,y) r11: app(i_0(),y) -> i_1(y) r12: app(map_0(),y) -> map_1(y) r13: app(map_1(x1),y) -> map_2(x1,y) r14: ._2(|1|_0(),x) -> x r15: ._2(x,|1|_0()) -> x r16: ._2(i_1(x),x) -> |1|_0() r17: ._2(x,i_1(x)) -> |1|_0() r18: ._2(i_1(y),._2(y,z)) -> z r19: ._2(y,._2(i_1(y),z)) -> z r20: i_1(|1|_0()) -> |1|_0() r21: i_1(i_1(x)) -> x r22: map_2(f,nil_0()) -> nil_0() r23: map_2(f,cons_2(x,xs)) -> cons_2(app(f,x),map_2(f,xs)) r24: filter_2(f,nil_0()) -> nil_0() r25: filter_2(f,cons_2(x,xs)) -> filter2_4(app(f,x),f,x,xs) r26: filter2_4(true_0(),f,x,xs) -> cons_2(x,filter_2(f,xs)) r27: filter2_4(false_0(),f,x,xs) -> filter_2(f,xs) The set of usable rules consists of (no rules) Take the reduction pair: generalized weighted path order (>=MG, >G) base order 1: matrix interpretation with standard point-wise order: carrier: N^1 order: standard order interpretations: map_2#_A(x1,x2) = x2 cons_2_A(x1,x2) = x1 + x2 + 2 base order 2: marked-algebra reduction triple (>=A, >=A!, >A!): max/plus interpretation on natural numbers: map_2#_A(x1,x2) = 0 cons_2_A(x1,x2) = max{4, x1 - 4, x2 - 4} map_2#!_A(x1,x2) = 6 cons_2!_A(x1,x2) = max{5, x1 - 17, x2 - 12} partial status: pi(map_2#) = [2] pi(cons_2) = [] The following rules are removed: p1 Then no dependency pair remains. -- Reduction pair. Consider the dependency pair problem (P, R), where P consists of p1: filter2_4#(false_0(),f,x,xs) -> filter_2#(f,xs) p2: filter_2#(f,cons_2(x,xs)) -> filter2_4#(app(f,x),f,x,xs) p3: filter2_4#(true_0(),f,x,xs) -> filter_2#(f,xs) and R consists of: r1: app(._0(),y) -> ._1(y) r2: app(._1(x1),y) -> ._2(x1,y) r3: app(cons_0(),y) -> cons_1(y) r4: app(cons_1(x1),y) -> cons_2(x1,y) r5: app(filter_0(),y) -> filter_1(y) r6: app(filter_1(x1),y) -> filter_2(x1,y) r7: app(filter2_0(),y) -> filter2_1(y) r8: app(filter2_1(x1),y) -> filter2_2(x1,y) r9: app(filter2_2(x1,x2),y) -> filter2_3(x1,x2,y) r10: app(filter2_3(x1,x2,x3),y) -> filter2_4(x1,x2,x3,y) r11: app(i_0(),y) -> i_1(y) r12: app(map_0(),y) -> map_1(y) r13: app(map_1(x1),y) -> map_2(x1,y) r14: ._2(|1|_0(),x) -> x r15: ._2(x,|1|_0()) -> x r16: ._2(i_1(x),x) -> |1|_0() r17: ._2(x,i_1(x)) -> |1|_0() r18: ._2(i_1(y),._2(y,z)) -> z r19: ._2(y,._2(i_1(y),z)) -> z r20: i_1(|1|_0()) -> |1|_0() r21: i_1(i_1(x)) -> x r22: map_2(f,nil_0()) -> nil_0() r23: map_2(f,cons_2(x,xs)) -> cons_2(app(f,x),map_2(f,xs)) r24: filter_2(f,nil_0()) -> nil_0() r25: filter_2(f,cons_2(x,xs)) -> filter2_4(app(f,x),f,x,xs) r26: filter2_4(true_0(),f,x,xs) -> cons_2(x,filter_2(f,xs)) r27: filter2_4(false_0(),f,x,xs) -> filter_2(f,xs) The set of usable rules consists of r1, r2, r3, r4, r5, r7, r8, r11, r12, r14, r15, r16, r17, r18, r19, r20, r21, r22, r24 Take the reduction pair: generalized weighted path order (>=MG, >G) base order 1: matrix interpretation with standard point-wise order: carrier: N^1 order: standard order interpretations: filter2_4#_A(x1,x2,x3,x4) = x4 + 6 false_0_A() = 1 filter_2#_A(x1,x2) = x2 + 5 cons_2_A(x1,x2) = x2 + 7 app_A(x1,x2) = x1 + x2 + 13 true_0_A() = 4 ._0_A() = 1 ._1_A(x1) = x1 + 2 ._2_A(x1,x2) = x1 + x2 + 1 cons_0_A() = 1 cons_1_A(x1) = x1 + 2 filter_0_A() = 1 filter_1_A(x1) = x1 + 2 filter2_0_A() = 3 filter2_1_A(x1) = x1 + 2 filter2_2_A(x1,x2) = x1 + x2 + 1 i_0_A() = 1 i_1_A(x1) = x1 + 2 map_0_A() = 1 map_1_A(x1) = x1 + 9 |1|_0_A() = 1 map_2_A(x1,x2) = x1 + 8 nil_0_A() = 1 filter_2_A(x1,x2) = x1 + x2 + 3 base order 2: marked-algebra reduction triple (>=A, >=A!, >A!): max/plus interpretation on natural numbers: filter2_4#_A(x1,x2,x3,x4) = max{1, x2 - 1, x3 - 29, x4 - 1} false_0_A = 17 filter_2#_A(x1,x2) = max{1, x1 - 1, x2 - 4} cons_2_A(x1,x2) = max{x1 - 25, x2 + 4} app_A(x1,x2) = max{24, x1 - 8, x2 + 9} true_0_A = 22 ._0_A = 0 ._1_A(x1) = x1 + 9 ._2_A(x1,x2) = max{24, x1 + 1, x2 + 1} cons_0_A = 0 cons_1_A(x1) = x1 + 7 filter_0_A = 0 filter_1_A(x1) = max{0, x1 - 26} filter2_0_A = 0 filter2_1_A(x1) = x1 filter2_2_A(x1,x2) = max{x1 - 8, x2} i_0_A = 0 i_1_A(x1) = max{22, x1} map_0_A = 0 map_1_A(x1) = x1 |1|_0_A = 24 map_2_A(x1,x2) = max{11, x1 - 8, x2 - 2} nil_0_A = 11 filter_2_A(x1,x2) = max{10, x1 - 34, x2} filter2_4#!_A(x1,x2,x3,x4) = max{6, x2 - 2, x3 - 30, x4 - 5} false_0!_A = 1 filter_2#!_A(x1,x2) = max{6, x1 - 2, x2 - 5} cons_2!_A(x1,x2) = max{5, x1 - 31, x2 - 43} app!_A(x1,x2) = max{7, x1 - 1, x2 - 27} true_0!_A = 2 ._0!_A = 2 ._1!_A(x1) = max{1, x1 - 28} ._2!_A(x1,x2) = max{9, x1 - 23, x2 - 27} cons_0!_A = 1 cons_1!_A(x1) = 2 filter_0!_A = 1 filter_1!_A(x1) = max{2, x1 - 27} filter2_0!_A = 9 filter2_1!_A(x1) = max{8, x1 - 28} filter2_2!_A(x1,x2) = max{9, x1 + 1, x2 - 3} i_0!_A = 1 i_1!_A(x1) = max{2, x1 - 28} map_0!_A = 1 map_1!_A(x1) = max{0, x1 - 28} |1|_0!_A = 0 map_2!_A(x1,x2) = max{0, x2 - 50} nil_0!_A = 4 filter_2!_A(x1,x2) = max{3, x1 - 27, x2 - 47} partial status: pi(filter2_4#) = [4] pi(false_0) = [] pi(filter_2#) = [] pi(cons_2) = [] pi(app) = [2] pi(true_0) = [] pi(._0) = [] pi(._1) = [1] pi(._2) = [] pi(cons_0) = [] pi(cons_1) = [] pi(filter_0) = [] pi(filter_1) = [1] pi(filter2_0) = [] pi(filter2_1) = [] pi(filter2_2) = [2] pi(i_0) = [] pi(i_1) = [] pi(map_0) = [] pi(map_1) = [1] pi(|1|_0) = [] pi(map_2) = [1] pi(nil_0) = [] pi(filter_2) = [] The following rules are removed: p1, p2, p3 Then no dependency pair remains.