diff --git a/tennis.c b/tennis.c
index fc56713..3148841 100644
--- a/tennis.c
+++ b/tennis.c
@@ -15,6 +15,9 @@ typedef uint64_t u64;
 #define LEN(a) (sizeof(a) / sizeofel(a))
 
 const char *lut[] = {
+    // characters within the same string are considered the same.
+    // that means the number of choices for a single character
+    // goes down from 36 to 28.
     "N", "P", "Q", "R",
     "T", "W", "X", "Y",
     "17I", "2Z", "5S", "8B",
@@ -114,6 +117,7 @@ int decode_data(code_t *code) {
 
     if (!check_ranges(code)) return 0;
 
+    // TODO: refactor so this isn't repeated in encode_data.
     const u32 neg1 = (u32)-1;
     if (code->data[2] == neg1 || code->data[2] != code->data[4]); else return 0;
     if (code->data[1] < 7 || (code->data[2] != neg1 && code->data[4] != neg1)); else return 0;
@@ -197,20 +201,41 @@ int bruteforce() { // with a fixed seed, this is useful for testing.
 
 int main(int argc, char **argv) {
     if (argc == 1) {
-        // self-test.
-        if (!validate_entry("48HWOR482")) return -1;
-        if (!validate_entry("5G3LTQ5GN")) return -1;
-        if (!validate_entry("A3W5KQA3C")) return -1;
-        if (!validate_entry("ARM6JQARU")) return -1;
-        if (!validate_entry("E8ULJRE8M")) return -1;
-        if (!validate_entry("J6M9PQJ6U")) return -1;
-        if (!validate_entry("LA98JRLAR")) return -1;
-        if (!validate_entry("M1C2YQM1W")) return -1;
-        if (!validate_entry("MM55MQMMJ")) return -1;
-        if (!validate_entry("N24K8QN2P")) return -1;
-        if (!validate_entry("OF9XFQOFR")) return -1;
-        if (!validate_entry("UOUFMPUOM")) return -1;
-        if (!validate_entry("V2UFMPUZM")) return -1;
+        // self-test with codes known before this program was written.
+#define TEST(entry) if (!validate_entry(entry)) return -1
+        TEST("48HWOR482");
+        TEST("5G3LTQ5GN");
+        //TEST("5PURGR5PM");
+        //TEST("6PJEGRGP5");
+        //TEST("8GYUHR86F");
+        TEST("A3W5KQA3C");
+        TEST("ARM6JQARU");
+        TEST("E880MPE8K");
+        TEST("E8ULJRE8M");
+        TEST("EPJEGREP5");
+        TEST("GH4KNQGHP");
+        TEST("H6L3MPH60");
+        TEST("HH4KNQHHP");
+        TEST("J6M9PQJ6U");
+        TEST("JEP8YQJE4");
+        TEST("LA98JRLAR");
+        TEST("LQM1MPLQU");
+        TEST("LTHWYQLT2");
+        TEST("M1C2YQM1W");
+        TEST("MM55MQMMJ");
+        TEST("N24K8QN2P");
+        TEST("OF9XFQOFR");
+        TEST("P4K6GRP48");
+        TEST("TE6WARTEQ");
+        TEST("TQJEGRTQ5");
+        TEST("UOUFMPUOM");
+        TEST("V2UFMPUZM");
+        TEST("W2HEGRW22");
+        TEST("WQJEGRWQ5");
+        TEST("WRWQARWRC");
+        TEST("YQJEGRYQ5");
+        //TEST("ZKZLZKNNR");
+#undef TEST
         return 0;
     }