/in/foo.cc: In function 'bool permutation(int)':
/in/foo.cc:40:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:177:8: warning: iteration 24 invokes undefined behavior [-Waggressive-loop-optimizations]
   k[i] = i;
   ~~~~~^~~
/in/foo.cc:176:22: note: within this loop
  for (R int i = 1; i <= 25; i++)
                    ~~^~~~~