Index: aoc2025.c
==================================================================
--- aoc2025.c
+++ aoc2025.c
@@ -40,35 +40,35 @@
                     *destin = '@';
                 }
             } else if (cc != 0) {
                 *destin = '.';
             } else {
-                *destin = 0; // shouldn't happen
+                *destin = 0; // shouldn't happen, except beyond borders
             }
         }
     }
     return changes;
 }
 
 void aoc202504(char *data, size_t len) {
     (void)len; // unused argument
     struct RectangularMap rm[2] = {0};
-    while (*data) {
+    while (*data) {                      // copy from data to rms
         char *data2 = data;
         while (*data != '\n') data++;
         *data = 0; // erase newline
         RMaddline(rm + 0, data2);
         RMaddline(rm + 1, data2); // set both rm's to the same thing
-        *data++ = '\n'; // unerase newline and skip it
+        *data++ = '\n'; // unerase newline (obviously!) and skip it
     }
     unsigned part1 = evolve(rm, 0); // evolve from rm[0] to rm[1]
     unsigned part2 = part1, src = 1;
     for (;;) {
         unsigned tmp = evolve(rm, src); // keep evolving
-        if (tmp == 0) break; // STOP
-        src = 1 - src;                  // back and forth
-        part2 += tmp; // add changes in this round
+        if (tmp == 0) break; // STOP    // back and forth
+        src = 1 - src;                  // between rm[1] and rm[0]
+        part2 += tmp; // add changes from this round
     }
     printf("P1: %u; P2: %u\n", part1, part2);
     RMfree(rm);
     RMfree(rm + 1);
 }