Contents 1. Introduction 2 2. Preliminaries 4 2.1. Some results on ...

Contents 1. Introduction 2 2. Preliminaries 4 2.1. Some results on ... Contents 1. Introduction 2 2. Preliminaries 4 2.1. Some results on ...

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136and hence we get(160) x ◦ (χP ) ◦ ( QP w l) = x ◦ (χP ) ◦ (QP w r ) .We observe thatν ′ 0 ◦ (m B P ) ◦ (ByP ) ◦ ( BP w l) ◦ (yP QP C)= ν ′ 0 ◦ (m B P ) ◦ (ByP ) ◦ (yP QP ) ◦ ( P QP w l)= ν ′ 0 ◦ (m B P ) ◦ (yyP ) ◦ ( P QP w l)(109)= ν ′ 0 ◦ (yP ) ◦ (P χP ) ◦ ( P QP w l)(149)= l ◦ (P x) ◦ (P χP ) ◦ ( P QP w l)(160)= l ◦ (P x) ◦ (P χP ) ◦ (P QP w r )(149)= ν ′ 0 ◦ (yP ) ◦ (P χP ) ◦ (P QP w r )(109)= ν ′ 0 ◦ (m B P ) ◦ (yyP ) ◦ (P QP w r )= ν ′ 0 ◦ (m B P ) ◦ (ByP ) ◦ (yP QP ) ◦ (P QP w r )= ν ′ 0 ◦ (m B P ) ◦ (ByP ) ◦ (BP w r ) ◦ (yP QP C)since yP QP C is an epimorphism, we obtain thatν 0 ′ ◦ (m B P ) ◦ (ByP ) ◦ ( BP w l) = ν 0 ′ ◦ (m B P ) ◦ (ByP ) ◦ (BP w r ) .(Since B preserves coequalizers, we have that B ̂Q,)Bν 0′ = Coequ Fun ((ByP ) ◦( ) BP wl, (ByP ) ◦ (BP w r )) so that there exists a unique functorial morphism B µb Q:( )̂Q, B µb QB ̂Q → ̂Q which satisfies (151).Now we want to show thatB-module functor. First let us prove that B µb Qis associative that is) ( )(B B µb Qm B ̂Q .B µb Q◦= B µb Q◦is a leftWe have)B µb Q◦(B B µb Q◦ (BBν ′ 0) (151)= B µb Q◦ (Bν ′ 0) ◦ (Bm B P )(151)= ν ′ 0 ◦ (m B P ) ◦ (Bm B P ) m Bass(151)= B µb Q◦ (Bν ′ 0) ◦ (m B BP ) m B= B µb Q◦= ν 0 ′ ◦ (m B P ) ◦ (m B BP )( )m B ̂Q ◦ (BBν 0) ′ .Since BBν 0 ′ is an epimorphism, we get that B µb Qis associative. Let us prove thatB µb Qis unital that is( )B µb Q◦ u B ̂Q = ̂Q.We calculate( )B µb Q◦ u B ̂Q◦ ν ′ 0 = B µb Q◦ (Bν ′ 0) ◦ (u B BP ) (151)= ν ′ 0 ◦ (m B P ) ◦ (u B BP ) = ν ′ 0.

Since ν 0 ′ is an epimorphism, we get that B µb Qis unital. Finally we have to prove thecompatibility condition) ( )(Bµ A Q b = µ A Q b ◦B µb QA .B µb Q◦137We haveB µb Q◦) (Bµ A Q b ◦ (BlA) ◦ (BP xx) ◦ (yP QP QP )(150)= B µb Q◦ (Bl) ◦ (BP m A ) ◦ (BP xx) ◦ (yP QP QP )(102)= B µb Q◦ (Bl) ◦ (BP x) ◦ (BP χP ) ◦ (yP QP QP )(149)= B µb Q◦ (Bν ′ 0) ◦ (ByP ) ◦ (BP χP ) ◦ (yP QP QP )y= B µb Q◦ (Bν ′ 0) ◦ (ByP ) ◦ (yP QP ) ◦ (P QP χP )= B µb Q◦ (Bν ′ 0) ◦ (yyP ) ◦ (P QP χP )(151)= ν ′ 0 ◦ (m B P ) ◦ (yyP ) ◦ (P QP χP )(109)= ν ′ 0 ◦ (yP ) ◦ (P χP ) ◦ (P QP χP )(98)= ν ′ 0 ◦ (yP ) ◦ (P χP ) ◦ (P χP QP )(149)= l ◦ (P x) ◦ (P χP ) ◦ (P χP QP )(102)= l ◦ (P m A ) ◦ (P xx) ◦ (P χP QP )= l ◦ (P m A ) ◦ (P xA) ◦ (P QP x) ◦ (P χP QP )χ= l ◦ (P m A ) ◦ (P xA) ◦ (P χP A) ◦ (P QP QP x)(150)= µ A b Q◦ (lA) ◦ (P xA) ◦ (P χP A) ◦ (P QP QP x)(149)= µ A b Q◦ (ν ′ 0A) ◦ (yP A) ◦ (P χP A) ◦ (P QP QP x)(109)= µ A b Q◦ (ν ′ 0A) ◦ (m B P A) ◦ (yyP A) ◦ (P QP QP x)= µ A b Q◦ (ν ′ 0A) ◦ (m B P A) ◦ (ByP A) ◦ (yP QP A) ◦ (P QP QP x)y= µ A Q b ◦ (ν 0A) ′ ◦ (m B P A) ◦ (ByP A) ◦ (BP QP x) ◦ (yP QP QP )( )(151)= µ A Q b ◦B µb QA ◦ (Bν 0A) ′ ◦ (ByP A) ◦ (BP QP x) ◦ (yP QP QP )( )(149)= µ A Q b ◦B µb QA ◦ (BlA) ◦ (BP xA) ◦ (BP QP x) ◦ (yP QP QP )( )= µ A Q b ◦B µb QA ◦ (BlA) ◦ (BP xx) ◦ (yP QP QP )Since (BlA) ◦ (BP xx) ◦ (yP QP QP ) is an epimorphism, we conclude. Then(̂Q, B µb Q, µ A b Q)is a B-A-bimodule functor.□

Since ν 0 ′ is an epimorphism, we get that B µb Qis unital. Finally we have to prove thecompatibility c<strong>on</strong>diti<strong>on</strong>) ( )(Bµ A Q b = µ A Q b ◦B µb QA .B µb Q◦137We haveB µb Q◦) (Bµ A Q b ◦ (BlA) ◦ (BP xx) ◦ (yP QP QP )(150)= B µb Q◦ (Bl) ◦ (BP m A ) ◦ (BP xx) ◦ (yP QP QP )(102)= B µb Q◦ (Bl) ◦ (BP x) ◦ (BP χP ) ◦ (yP QP QP )(149)= B µb Q◦ (Bν ′ 0) ◦ (ByP ) ◦ (BP χP ) ◦ (yP QP QP )y= B µb Q◦ (Bν ′ 0) ◦ (ByP ) ◦ (yP QP ) ◦ (P QP χP )= B µb Q◦ (Bν ′ 0) ◦ (yyP ) ◦ (P QP χP )(151)= ν ′ 0 ◦ (m B P ) ◦ (yyP ) ◦ (P QP χP )(109)= ν ′ 0 ◦ (yP ) ◦ (P χP ) ◦ (P QP χP )(98)= ν ′ 0 ◦ (yP ) ◦ (P χP ) ◦ (P χP QP )(149)= l ◦ (P x) ◦ (P χP ) ◦ (P χP QP )(102)= l ◦ (P m A ) ◦ (P xx) ◦ (P χP QP )= l ◦ (P m A ) ◦ (P xA) ◦ (P QP x) ◦ (P χP QP )χ= l ◦ (P m A ) ◦ (P xA) ◦ (P χP A) ◦ (P QP QP x)(150)= µ A b Q◦ (lA) ◦ (P xA) ◦ (P χP A) ◦ (P QP QP x)(149)= µ A b Q◦ (ν ′ 0A) ◦ (yP A) ◦ (P χP A) ◦ (P QP QP x)(109)= µ A b Q◦ (ν ′ 0A) ◦ (m B P A) ◦ (yyP A) ◦ (P QP QP x)= µ A b Q◦ (ν ′ 0A) ◦ (m B P A) ◦ (ByP A) ◦ (yP QP A) ◦ (P QP QP x)y= µ A Q b ◦ (ν 0A) ′ ◦ (m B P A) ◦ (ByP A) ◦ (BP QP x) ◦ (yP QP QP )( )(151)= µ A Q b ◦B µb QA ◦ (Bν 0A) ′ ◦ (ByP A) ◦ (BP QP x) ◦ (yP QP QP )( )(149)= µ A Q b ◦B µb QA ◦ (BlA) ◦ (BP xA) ◦ (BP QP x) ◦ (yP QP QP )( )= µ A Q b ◦B µb QA ◦ (BlA) ◦ (BP xx) ◦ (yP QP QP )Since (BlA) ◦ (BP xx) ◦ (yP QP QP ) is an epimorphism, we c<strong>on</strong>clude. Then(̂Q, B µb Q, µ A b Q)is a B-A-bimodule functor.□

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