-generation *generations; /* all the generations */
-generation *g0; /* generation 0, for convenience */
-generation *oldest_gen; /* oldest generation, for convenience */
-step *g0s0; /* generation 0, step 0, for convenience */
+generation *generations = NULL; /* all the generations */
+generation *g0 = NULL; /* generation 0, for convenience */
+generation *oldest_gen = NULL; /* oldest generation, for convenience */
+step *g0s0 = NULL; /* generation 0, step 0, for convenience */