WORKAROUND: Avoid problems in Kan package.

The Kan package copied library code and thus uses undocumented entries
of rewriting systems. Added workaround to avoid triggering an error
in the test.

This resolves #5478

lib/kbsemi.gi

@@ -182,6 +182,9 @@ DeclareRepresentation("IsKnuthBendixRewritingSystemRep",
 ##  refers to one of the rules. A pair corresponds to a pair
 ##  of rules where confluence was not yet checked (according to
 ##  the Knuth Bendix algorithm).
+##  Pairs might also be given in the form of a 3-entry list
+##  ['A',x,l] to denote all pairs of the form [x,y] for y in l,
+##  respectively ['B',l,y] for pairs [x,y[] with x in l.
 ##
 ##  Note that at this stage the kb rws obtained might not be reduced
 ##  (the same relation might even appear several times).
@@ -767,6 +770,22 @@ function ( rws )
        " rules" );
 end);
 
+# We store compressed data -- expand, (and also delete old stuff)
+BindGlobal("KBRWSUnpackPairsAt",function(kbrws,p)
+local i,a;
+  i:=kbrws!.pairs2check[p];
+  if IsChar(i[1]) then
+    # We store compressed data -- expand, (and also delete old stuff)
+    if i[1]='A' then
+      a:=List(i[3],x->[i[2],x]);
+    elif i[1]='B' then
+      a:=List(i[2],x->[x,i[3]]);
+    else Error("kind"); fi;
+    kbrws!.pairs2check:=Concatenation(a,kbrws!.pairs2check{[p+1..Length(kbrws!.pairs2check)]});
+    p:=1;
+  fi;
+  return p;
+end);
 
 
 
@@ -776,7 +795,15 @@ end);
 BindGlobal("KBOverlaps",function(ui,vi,kbrws,p)
 local u,v,m,k,a,c,lsu,lsv,lu,eq,i,j;
 
+  # work around copied code in kan package
+  if IsChar(ui) then # must unpack
+    p:=KBRWSUnpackPairsAt(kbrws,p);
+    vi:=kbrws!.pairs2check[p];
+    ui:=vi[1];vi:=vi[2];
+  fi;
+
   u:=kbrws!.tzrules[ui]; v:=kbrws!.tzrules[vi];
+
   lsu:=u[1];
   lu:=Length(lsu);
   lsv:=v[1];
@@ -860,15 +887,7 @@ local   pn,lp,rl,p,i,a;
     i:=kbrws!.pairs2check[p];
     if IsChar(i[1]) then
       # We store compressed data -- expand, (and also delete old stuff)
-      if i[1]='A' then
-        a:=List(i[3],x->[i[2],x]);
-      elif i[1]='B' then
-        a:=List(i[2],x->[x,i[3]]);
-      else Error("kind"); fi;
-      kbrws!.pairs2check:=Concatenation(a,kbrws!.pairs2check{[p+1..Length(kbrws!.pairs2check)]});
-      p:=1;
-      i:=kbrws!.pairs2check[p];
-      lp:=Length(kbrws!.pairs2check);
+      p:=KBRWSUnpackPairsAt(kbrws,p);
     fi;
 
     p:=KBOverlaps(i[1],i[2],kbrws,p)+1;