Compilation error with the `log()` function.

overridden-log-error.txt

$ make
gcc -g -DIMPL_SECURITY -DNEW_RENT -DLEVEL_LOSS -DNEWEXP -DGROUP_NAMES -DIMPL_SECURITY -DNEW_RENT -DLEVEL_LOSS -DNEWEXP -DGROUP_NAMES  -c -o comm.o comm.c
comm.c:133:7: warning: implicitly declaring library function 'log' with type
      'double (double)'
      log("Lawful mode selected.");
      ^
comm.c:133:7: note: please include the header <math.h> or explicitly provide a
      declaration for 'log'
...