Minor changes made to SwapDigraphs and DigraphRemoveAllEdges doc

Author: rm387

doc/attr.xml

@@ -2097,9 +2097,8 @@ gap> D;
   <Attr Name="DigraphRemoveAllEdgesAttr" Arg="digraph"/>
   <Returns>An empty digraph.</Returns>
   <Description>
-    This operation returns a digraph constructed from <A>digraph</A>, which is mutable,
-    by removing all of the edges in the original digraph
-    (see <Ref Oper="DigraphRemoveEdge" Label="for a digraph and an edge"/>).
+    This operation returns a digraph constructed from <A>digraph</A>. If <A>digraph</A> is mutable, 
+    its list of neighbours will be replaced with an empty 2D list of the same length. 
     <P/>
 
     If <A>digraph</A> is immutable, then a new, empty immutable digraph with the same number of vertices is returned.
@@ -2109,7 +2108,6 @@ gap> D3 := Digraph(IsMutableDigraph, [[2], [1], [2]]);
 <mutable digraph with 3 vertices, 3 edges>
 gap> DigraphRemoveAllEdges(D3);
 <mutable empty digraph with 3 vertices>
-true
 ]]></Example>
   </Description>
 </ManSection>

gap/oper.gi

@@ -990,7 +990,7 @@ function(D1, D2, edge_function)
 end);
 
 InstallMethod(SwapDigraphs,
-"for a mutable digraph and mutable digraph",
+"for two mutable digraphs",
 [IsMutableDigraph, IsMutableDigraph],
 function(D1, D2)
   local nb1, nb2;