Fix for computing quotients of certain algebra modules

The issue was originally reported by Rudolf Tange on the GAP
support mailing list.

lib/algrep.gi

@@ -3177,6 +3177,19 @@ InstallMethod( Coefficients,
 end );
 
 
+#############################################################################
+##
+#M  \in( <V>, <v> )
+##
+InstallMethod( \in,
+    "for vector and a sparse rowspace",
+    IsElmsColls,
+    [ IsSparseRowSpaceElement, IsFreeLeftModule and IsSparseRowSpaceElementCollection ],
+    function( v, V )
+    return Coefficients(Basis(V),v) <> fail;
+    end );
+
+
 #############################################################################
 ##
 #M  FullSparseRowSpace( <F>, <n> )  . . . . . . for a ring and an integer

tst/testinstall/algrep.tst

@@ -0,0 +1,19 @@
+gap> START_TEST("algrep.tst");
+
+#
+gap> L:=FullMatrixLieAlgebra(GF(5),2);
+<Lie algebra over GF(5), with 3 generators>
+gap> V:=AdjointModule(L);
+<left-module over <Lie algebra over GF(5), with 3 generators>>
+gap> s:=List([0..3],r->SymmetricPowerOfAlgebraModule(V,r));;
+gap> V:=DirectSumOfAlgebraModules(s);
+<35-dimensional left-module over <Lie algebra over GF(5), with 3 generators>>
+gap> BV:=Basis(V);;
+gap> lst:=[BV[5]];;
+gap> W:=SubAlgebraModule(V,lst,"basis");
+<1-dimensional left-module over <Lie algebra over GF(5), with 3 generators>>
+gap> V/W;
+<34-dimensional left-module over <Lie algebra over GF(5), with 3 generators>>
+
+#
+gap> STOP_TEST( "algrep.tst", 1);