<Chapter><Heading> G-Outer Groups</Heading> <Table Align="|l|" > <Row> <Item> <Index>GOuterGroup</Index> <C>GOuterGroup(E,N)</C> <Br/> <C>GOuterGroup()</C> <P/> Inputs a group <M>E</M> and normal subgroup <M>N</M>. It returns <M>N</M> as a <M>G</M>-outer group where <M>G=E/N</M>. <P/> The function can be used without an argument. In this case an empty outer group <M>C</M> is returned. The components must be set using SetActingGroup(C,G), SetActedGroup(C,N) and SetOuterAction(C,alpha). </Item> </Row> <Row> <Item> <Index>GOuterGroupHomomorphismNC</Index> <C>GOuterGroupHomomorphismNC(A,B,phi)</C> <Br/> <C>GOuterGroupHomomorphismNC()</C> <P/> Inputs G-outer groups <M>A</M> and <M>B</M> with common acting group, and a group homomorphism phi:ActedGroup(A) --> ActedGroup(B). It returns the corresponding G-outer homomorphism PHI:A--> B. No check is made to verify that phi is actually a group homomorphism which preserves the G-action. <P/> The function can be used without an argument. In this case an empty outer group homomorphism <M>PHI</M> is returned. The components must then be set. </Item> </Row> <Row> <Item> <Index>GOuterHomomorphismTester</Index> <C>GOuterHomomorphismTester(A,B,phi)</C> <P/> Inputs G-outer groups <M>A</M> and <M>B</M> with common acting group, and a group homomorphism phi:ActedGroup(A) --> ActedGroup(B). It tests whether phi is a group homomorphism which preserves the G-action. <P/> The function can be used without an argument. In this case an empty outer group homomorphism <M>PHI</M> is returned. The components must then be set. </Item> </Row> <Row> <Item> <Index>Centre</Index> <C>Centre(A)</C> <P/> Inputs G-outer group <M>A</M> and returns the group theoretic centre of ActedGroup(A) as a G-outer group. </Item> </Row> <Row> <Item> <Index>DirectProductGog</Index> <C>DirectProductGog(A,B)</C> <Br/> <C>DirectProductGog(Lst)</C> <P/> Inputs G-outer groups <M>A</M> and <M>B</M> with common acting group, and returns their group-theoretic direct product as a G-outer group. The outer action on the direct product is the diagonal one. <P/> The function also applies to a list Lst of G-outer groups with common acting group. <P/> For a direct product D constructed using this function, the embeddings and projections can be obtained (as G-outer group homomorphisms) using the functions Embedding(D,i) and Projection(D,i). </Item> </Row> </Table> </Chapter>