go =>
  Strings = [
                 "1001110011",       % 10011
                 "1110111011",       % 1110
                 "0010010010",       % 001
                 "1010101010",       % 1010
                 "1111111111",       % 11111
                 "0100101101",       % no solution
                 "0100100",          % 010
                 "101",              % no solution
                 "11",               % 1
                 "00",               % 0
                 "1",                % no solution
                 "",                 % no solution
                 "123123123123123",  % 123123
                 "12312312312312",   % 123123
                 "123123123123124",  % no solution
                 "abcabcdabcabcdabc", % abcabcd
                 [1,2,3,4,1,2,3,4,1,2,3] % 1,2,3,4

            ],
  foreach(S in Strings)
    printf("%w: ", S),
    if maxrep(S,Substr,N) then
      println([substr=Substr,n=N])
    else
      println("no solution")
    end
  end,
  nl.

% the largest repeating substring
maxrep(S,Substr,N) =>
  maxof(rep(S,Substr,N),N).

rep(S,Substr,N) =>
  between(1,S.length div 2, N),
  Len = S.length,
  Len2 = Len - (Len mod N),
  Substr = slice(S,1,N),
  % count the number of proper slices
  SS = [1 : I in 1..N..Len2, slice(S,I,I+N-1) = Substr],
  SS.length = Len div N,
  % the last (truncated) slice (or []) must be a substring of Substr
  Rest = slice(S,Len2+1,Len),
  find(Substr,Rest,1,_).