Replace some uses of FOO[Length(FOO)] by Last(FOO)

hpcgap/lib/cmdleditx.g

@@ -125,7 +125,7 @@
   hist := CommandLineHistory;
   if key = 0 then  # save line data
     # no trailing white space
-    while Length(l[1]) > 0 and l[1][Length(l[1])] in "\n\r\t " do
+    while Length(l[1]) > 0 and Last(l[1]) in "\n\r\t " do
       Remove(l[1]);
     od;
     MaxCommandLineHistory := UserPreference("HistoryMaxLines");

lib/ctbl.gi

@@ -1231,7 +1231,7 @@
 InstallGlobalFunction( CharacterTable_IsNilpotentFactor, function( tbl, N )
     local series;
     series:= CharacterTable_UpperCentralSeriesFactor( tbl, N );
-    return Length( series[ Length( series ) ] ) = NrConjugacyClasses( tbl );
+    return Length( Last(series) ) = NrConjugacyClasses( tbl );
     end );
 
 
@@ -1245,7 +1245,7 @@
     function( tbl )
     local series;
     series:= ClassPositionsOfUpperCentralSeries( tbl );
-    return Length( series[ Length( series ) ] ) = NrConjugacyClasses( tbl );
+    return Length( Last(series) ) = NrConjugacyClasses( tbl );
     end );
 
 
@@ -3300,7 +3300,7 @@
           if i = r[1] or i-1 in hlines then
             Append( str, " \\rule[0pt]{0pt}{13pt}" );
           fi;
-          if i = r[ Length( r ) ] or i in hlines then
+          if i = Last(r) or i in hlines then
             Append( str, " \\rule[-7pt]{0pt}{5pt}" );
           fi;
 
@@ -4712,7 +4712,7 @@
         n:= QuoInt(n-1, ll);
       od;
       Add( irrnames, name );
-      return irrnames[ Length( irrnames ) ];
+      return name;
 
     elif    ( IsList( entry ) and not IsString( entry ) )
          or IsUnknown( entry ) then
@@ -5430,7 +5430,7 @@
             for j in [ 1 .. Length( info ) - 1 ] do
               Print( "\"", info[j], "\\n\",\n" );
             od;
-            Print( "\"", info[ Length( info ) ], "\"\n]);\n" );
+            Print( "\"", Last(info), "\"\n]);\n" );
           else
             Print( "\"", info, "\";\n" );
           fi;
@@ -7001,7 +7001,7 @@
 
     # Check the arguments.
     if not ( Length( arg ) in [ 2, 3 ] and IsOrdinaryTable( arg[1] ) and
-             IsList( arg[ Length( arg ) ] ) and
+             IsList( Last(arg) ) and
              ( Length( arg ) = 2 or IsOrdinaryTable( arg[2] ) ) ) then
       Error( "usage: SortedCharacterTable( <tbl>, <kernel> ) resp.\n",
              "       SortedCharacterTable( <tbl>, <normalseries> ) resp.\n",
@@ -7048,7 +7048,7 @@
       # if the `i'--th irreducible contains none of `kernels' in its kernel,
       # we have `list[i] = -1',
       # for an irreducible with kernel containing
-      # `kernels[ Length( kernels ) ]',
+      # `Last(kernels)',
       # the value is `-(Length( kernels ) + 1)'.
       list:= [];
       if HasIrr( tbl ) then

lib/gpfpiso.gi

@@ -2623,7 +2623,7 @@
           if IsOddInt(i) then x:=(i+1)/2;
           else x:=-i/2;fi;
           # word must be freely cancelled
-          if Length(g)>0 and x=-g[Length(g)] then
+          if Length(g)>0 and x=-Last(g) then
             Remove(g);
           else Add(g,x); fi;
         od;

lib/grp.gi

@@ -602,7 +602,7 @@
     S := LowerCentralSeriesOfGroup( G );
 
     # <G> is nilpotent if the lower central series reaches the trivial group
-    return IsTrivial( S[ Length( S ) ] );
+    return IsTrivial( Last(S) );
     end );
 
 
@@ -710,7 +710,7 @@
     fi;
 
     der:= DerivedSeriesOfGroup( G );
-    der:= der[ Length( der ) ];
+    der:= Last(der);
     if IsTrivial( der ) then
       return false;
     fi;
@@ -797,7 +797,7 @@
     S := DerivedSeriesOfGroup( G );
 
     # the group is solvable if the derived series reaches the trivial group
-    isSolvable := IsTrivial( S[ Length( S ) ] );
+    isSolvable := IsTrivial( Last(S) );
 
     # set IsAbelian filter
     isAbelian := isSolvable and Length( S ) <= 2;
@@ -1017,16 +1017,16 @@
   od;
   while i<=Length(ser) and not IsSubset(sub,ser[i]) do
     c:=ClosureGroup(sub,ser[i]);
-    if Size(new[Length(new)])>Size(c) then
+    if Size(Last(new))>Size(c) then
       Add(new,c);
     fi;
-    if Size(new[Length(new)])>Size(ser[i]) then
+    if Size(Last(new))>Size(ser[i]) then
       Add(new,ser[i]);
     fi;
     sub:=Intersection(sub,ser[i]);
     i:=i+1;
   od;
-  if Size(sub)<Size(new[Length(new)]) and i<=Length(ser) and Size(sub)>Size(ser[i]) then
+  if Size(sub)<Size(Last(new)) and i<=Length(ser) and Size(sub)>Size(ser[i]) then
     Add(new,sub);
   fi;
   while i<=Length(ser) do
@@ -1087,7 +1087,7 @@
         TryNextMethod();
     fi;
     der := DerivedSeriesOfGroup(grp);
-    if not IsTrivial(der[Length(der)])  then
+    if not IsTrivial(Last(der))  then
         TryNextMethod();
     fi;
 
@@ -1153,9 +1153,9 @@
       rev:=[j];
       i:=post-1;
       repeat
-        if not IsSubset(rev[Length(rev)],cs[i]) then
+        if not IsSubset(Last(rev),cs[i]) then
           c:=ClosureGroup(cs[i],j);
-          if Size(c)>Size(rev[Length(rev)]) then
+          if Size(c)>Size(Last(rev)) then
             # proper down step
             Add(rev,c);
           fi;
@@ -1167,9 +1167,9 @@
 
       i:=pre;
       repeat
-        if not IsSubset(cs[i],new[Length(new)]) then
+        if not IsSubset(cs[i],Last(new)) then
           c:=Intersection(cs[i],j);
-          if Size(c)<Size(new[Length(new)]) then
+          if Size(c)<Size(Last(new)) then
             # proper down step
             Add(new,c);
           fi;
@@ -1223,6 +1223,7 @@
     [ IsGroup ],
     function ( G )
     local   S,          # derived series of <G>, result
+            lastS,      # last element of S
             D;          # derived subgroups
 
     # print out a warning for infinite groups
@@ -1234,26 +1235,28 @@
 
     # compute the series by repeated calling of `DerivedSubgroup'
     S := [ G ];
+    lastS := G;
     Info( InfoGroup, 2, "DerivedSeriesOfGroup: step ", Length(S) );
     D := DerivedSubgroup( G );
 
     while
-      (not HasIsTrivial(S[Length(S)]) or
-            not IsTrivial(S[Length(S)])) and
+      (not HasIsTrivial(lastS) or
+            not IsTrivial(lastS)) and
       (
-        (not HasIsPerfectGroup(S[Length(S)]) and
-         not HasAbelianInvariants(S[Length(S)]) and D <> S[ Length(S) ]) or
-        (HasIsPerfectGroup(S[Length(S)]) and not IsPerfectGroup(S[Length(S)]))
-        or (HasAbelianInvariants(S[Length(S)])
-                            and Length(AbelianInvariants(S[Length(S)])) > 0)
+        (not HasIsPerfectGroup(lastS) and
+         not HasAbelianInvariants(lastS) and D <> lastS) or
+        (HasIsPerfectGroup(lastS) and not IsPerfectGroup(lastS))
+        or (HasAbelianInvariants(lastS)
+                            and Length(AbelianInvariants(lastS)) > 0)
       ) do
         Add( S, D );
+        lastS := D;
         Info( InfoGroup, 2, "DerivedSeriesOfGroup: step ", Length(S) );
         D := DerivedSubgroup( D );
     od;
 
     # set filters if the last term is known to be trivial
-    if HasIsTrivial(S[Length(S)]) and IsTrivial(S[Length(S)]) then
+    if HasIsTrivial(lastS) and IsTrivial(lastS) then
       SetIsSolvableGroup(G, true);
       if Length(S) <=2 then
         Assert(3, IsAbelian(G));
@@ -1617,7 +1620,7 @@
     S := [ G ];
     Info( InfoGroup, 2, "LowerCentralSeriesOfGroup: step ", Length(S) );
     C := DerivedSubgroup( G );
-    while C <> S[ Length(S) ]  do
+    while C <> Last(S) do
         Add( S, C );
         Info( InfoGroup, 2, "LowerCentralSeriesOfGroup: step ", Length(S) );
         C := CommutatorSubgroup( G, C );
@@ -2331,15 +2334,15 @@
     S := [ TrivialSubgroup( G ) ];
     Info( InfoGroup, 2, "UpperCentralSeriesOfGroup: step ", Length(S) );
     C := Centre( G );
-    while C <> S[ Length(S) ]  do
+    while C <> Last(S) do
         Add( S, C );
         Info( InfoGroup, 2, "UpperCentralSeriesOfGroup: step ", Length(S) );
         hom := NaturalHomomorphismByNormalSubgroupNC( G, C );
         C := PreImages( hom, Centre( Image( hom ) ) );
     od;
 
-    if S[ Length(S) ] = G then
-        UseIsomorphismRelation( G, S[ Length(S) ] );
+    if Last(S) = G then
+        UseIsomorphismRelation( G, Last(S) );
     fi;
     # return the series when it becomes stable
     return Reversed( S );
@@ -2977,7 +2980,7 @@
     local ser;
 
     ser := LowerCentralSeriesOfGroup( G );
-    return Size ( ser[ Length( ser ) ] ) mod p <> 0;
+    return Size( Last(ser) ) mod p <> 0;
     end );
 
 RedispatchOnCondition (IsPNilpotentOp, ReturnTrue, [IsGroup, IsPosInt], [IsFinite], 0);
@@ -3336,13 +3339,13 @@
     for j in p do
       u:=ClosureGroup(u,SylowSubgroup(d[i-1],j));
       #force elementary
-      while not ForAll(GeneratorsOfGroup(u),x->x^j in loc[Length(loc)]) do
-        r:=NaturalHomomorphismByNormalSubgroupNC(u,loc[Length(loc)]);
+      while not ForAll(GeneratorsOfGroup(u),x->x^j in Last(loc)) do
+        r:=NaturalHomomorphismByNormalSubgroupNC(u,Last(loc));
         Pker:=Omega(Range(r),j,1);
         r:=PreImage(r,Pker);
         Add(loc,r);
       od;
-      if Size(u)<Size(ser[Length(ser)]) then
+      if Size(u)<Size(Last(ser)) then
         Add(loc,u);
       fi;
     od;
@@ -3371,7 +3374,7 @@
     S := [ G ];
     Info( InfoGroup, 2, "SubnormalSeries: step ", Length(S) );
     C := NormalClosure( G, U );
-    while C <> S[ Length( S ) ]  do
+    while C <> Last(S)  do
         Add( S, C );
         Info( InfoGroup, 2, "SubnormalSeries: step ", Length(S) );
         C := NormalClosure( C, U );
@@ -3392,7 +3395,7 @@
 function ( G, U )
 local s;
   s:=SubnormalSeries(G,U);
-  return U=s[Length(s)];
+  return U=Last(s);
 end);
 
 

lib/grpfp.gi

@@ -4772,7 +4772,7 @@ local g,i,x;
       x:=-i/2;
     fi;
     # free cancellation
-    if Length(g)>0 and x=-g[Length(g)] then
+    if Length(g)>0 and x=-Last(g) then
       Remove(g);
     else
       Add(g,x);

lib/grplatt.gi

@@ -1325,7 +1325,7 @@
   [IsGroup],0,
 function(G)
   G := DerivedSeriesOfGroup(G);
-  G := G[Length(G)];
+  G := Last(G);
   SetIsPerfectGroup(G, true);
   return G;
 end);
@@ -2052,7 +2052,7 @@
                   vs:=[];
                   if Length(mat)>0 then
                     for k in AsList(VectorSpace(ocr.field,mat)) do
-                      if IsOne(k[Length(k)]) then
+                      if IsOne(Last(k)) then
                         Add(vs,k{[1..Length(vsb)]}*vsb);
                       fi;
                     od;
@@ -3874,22 +3874,22 @@
 
               if Length(l)=0 then
                 # no groups there. Start getting new ones
-                a:=Filtered(process,x->Size(x)>=divs[Length(divs)]);
-                process:=Filtered(process,x->Size(x)<divs[Length(divs)]);
+                a:=Filtered(process,x->Size(x)>=Last(divs));
+                process:=Filtered(process,x->Size(x)<Last(divs));
                 for j in a do
                   m:=maxer(j);
                   Append(l,m);
                 od;
                 SortBy(l,Size);
               fi;
 
-              if Size(l[Length(l)])<divs[Length(divs)] then
+              if Size(Last(l))<Last(divs) then
                 # new size.
 
                 if Length(process)>0
-                 and Size(process[Length(process)])<=limit then
+                 and Size(Last(process))<=limit then
                   # switch to lattice
-                  a:=Size(l[Length(l)]);
+                  a:=Size(Last(l));
                   Info(InfoLattice,1,"get full lattice @size ",a);
                   l:=List(ConjugacyClassesSubgroups(G),Representative);
                   l:=Filtered(l,x->Size(x)<=a and
@@ -3900,7 +3900,7 @@
                 fi;
 
                 while Length(process)>0
-                 and Size(process[Length(process)])>=Maximum(List(l,Size)) do
+                 and Size(Last(process))>=Maximum(List(l,Size)) do
                   # need to process those that could give next size (or
                   # larger)
                   a:=Remove(process);
@@ -3910,14 +3910,14 @@
                 SortBy(l,Size);
 
                 # delete the orders not used any more
-                while Length(l)>0 and Size(l[Length(l)])<divs[Length(divs)] do
+                while Length(l)>0 and Size(Last(l))<Last(divs) do
                   Remove(divs); # sizes still in play
                 od;
                 done:=[]; # can ignore anything larger
 
                 if mode=1 then
-                  a:=Filtered(l,x->Size(x)=divs[Length(divs)]);
-                  l:=Filtered(l,x->Size(x)<divs[Length(divs)]);
+                  a:=Filtered(l,x->Size(x)=Last(divs));
+                  l:=Filtered(l,x->Size(x)<Last(divs));
                   a:=List(SubgroupsOrbitsAndNormalizers(G,a,false),
                     x->x.representative);
                   Append(l,a);

lib/grppcatr.gi

@@ -591,7 +591,7 @@ BindGlobal( "MinimalGensLayer", function( pcgs, pcgsS, pcgsN, min )
         if Length( pcgsM ) <> Length( pcgsL ) then
             Add( series, pcgsM );
         fi;
-        pcgsL := series[Length(series)];
+        pcgsL := Last(series);
 
         # modify minimal gens
         ModifyMinGens( pcgs, pcgsS, pcgsL, min );