Forum,
According to Devon Roy Stoddart:
> I have been trying to install Gap3, but I keep getting the remark " cannot
> find lib/init.g" even though it is there.

The most likely causes are:

1) You are starting GAP 3 by executing the binary directly, and not
using the gap.sh script which sets paths to the lib and doc directories
(among other things). I really think this is your problem.
In .../gap3r4p4/bin you should have:

>gap # The binary
>gap.bat # DOS script
>gap.sh # UNIX shell script

I'm assuming you run on a UNIX system so that
GAP 3 should be run by executing the gap.sh script
(on a DOS/Windows system you should do the equivalent with gap.bat)
i.e. if you have a symbolic link to gap from /usr/local/bin (or
wherever), make sure it points to gap.sh and *not* the gap binary.
e.g. on one system I have GAP 3 installed in directory:

>/usr/local/lib/gap/gap3r4p4

Since I now prefer to use GAP 4, my symbolic link in /usr/local/bin is
gap3 i.e. I did:

>cd /usr/local/bin
>ln -s /usr/local/lib/gap/gap3r4p4/bin/gap.sh gap3

... and since /usr/local/bin is in my path on that system, I run GAP 3
there by typing:

>gap3

Of course, you need to look at the gap.sh script and check that the
path GAP_DIR, in particular, is correct. Usually, the install process
guesses correctly.

2) If 1) is not the problem, the permissions of lib/init.g may be wrong
i.e. it isn't readable by you.
The subdirectories of .../gap3r4p4 should normally be executable and
readable by everyone e.g. an `ls -l' of .../gap3r4p4 should give
something like:

drwxr-xr-x  18 root     root         1024 May 21 11:59 ./
drwxr-xr-x   8 root     root         1024 May  6 20:58 ../
drwxr-xr-x   2 root     root         1024 May 21 12:14 bin/
.
.

If this isn't the case do a `chmod 755' of all directories with
wrong permissions.

Also the files in the subdirectories should normally be readable
by everyone e.g. an `ls -l' of .../gap3r4p4/lib/init.g should give
something like:

-rw-r--r--   1 root     root        50456 Apr 15  1997 init.g

I basically want to get the generators of the group formed by

F3 := FreeGroup("a","b","c");
S3 := F3 / [F3.2^-1*F3.3*F3.2^-1*F3.3*F3.1*F3.2^-1*F3.1,
	      F3.3^-1*F3.1*F3.3^-1*F3.1*F3.2*F3.3^-1*F3.2,
            F3.1^-1*F3.2*F3.1^-1*F3.2*F3.3*F3.1^-1*F3.3];

a := S3.1;; b := S3.2;; c := S3.3;;
presentationDerivedSubgroupFpGroup := function(S3)
  local comms, gens,h,i,j,ngens,pres;
  gens := S3.generators;
  ngens := Length(gens);
  comms := [];
  for i in [1..ngens-1] do
    for j in [i + 1 .. ngens] do
      Add(comms, Comm(gens[i],gens[j]));
    od;
  od;
  h := Subgroup(S3, comms);
  pres := PresentationNormalClosureRrs(S3,h);
  TzGoGo(pres);
  return(pres);
end;

I think you simply use TzPrintGenerators(pres);
or you assign the function to a variable
m := presentationDerivedSubgroupFpGroup(S3);
then TzPrintGenerators(m);

I ran the above with GAP 3, with the following result:

gap> F3 := FreeGroup("a","b","c");
Group( a, b, c )
gap> S3 := F3 / [F3.2^-1*F3.3*F3.2^-1*F3.3*F3.1*F3.2^-1*F3.1,
>               F3.3^-1*F3.1*F3.3^-1*F3.1*F3.2*F3.3^-1*F3.2,
>             F3.1^-1*F3.2*F3.1^-1*F3.2*F3.3*F3.1^-1*F3.3];
Group( a, b, c )
gap> 
gap> a := S3.1;; b := S3.2;; c := S3.3;;
gap> presentationDerivedSubgroupFpGroup := function(S3)
>   local comms, gens,h,i,j,ngens,pres;
>   gens := S3.generators;
>   ngens := Length(gens);
>   comms := [];
>   for i in [1..ngens-1] do
>     for j in [i + 1 .. ngens] do
>       Add(comms, Comm(gens[i],gens[j]));
>     od;
>   od;
>   h := Subgroup(S3, comms);
>   pres := PresentationNormalClosureRrs(S3,h);
>   TzGoGo(pres);
>   return(pres);
> end;
function ( S3 ) ... end
gap> m := presentationDerivedSubgroupFpGroup(S3);
#I  there are 5 generators and 6 relators of total length 119
<< presentation with 5 gens and 6 rels of total length 119 >>
gap> TzPrintGenerators(m);
#I  1.  _x4   23 occurrences
#I  2.  _x6   29 occurrences
#I  3.  _x11   21 occurrences
#I  4.  _x23   18 occurrences
#I  5.  _x24   28 occurrences
gap> 

If there is anyone who know the know how the correct the problem with the
init.g, I would appreciate getting the solution. However, if there is no
immediate solution and there is someone with gap3 already install and can
simply run a copy of the above function, I would truly appreciate it.
Additionally, I understand ElementaryDivisorsMat is still the same in Gap4
as is in gap3.

The above runs identically on GAP 4, provided you make the following change:

Replace the line:

gens := S3.generators;

with

gens := GeneratorsOfGroup(S3);

Regards,
Greg Gamble