Index: aoc2025.c
==================================================================
--- aoc2025.c
+++ aoc2025.c
@@ -13,10 +13,53 @@
 void aocYYYYDD(char *data, size_t len) {
     (void)len; // unused argument
 }
 
 #endif
+
+/* === aoc202507 =======================================================
+===================================================================== */
+static unsigned tachyon_splits(struct RectangularMap *rm) {
+    unsigned count = 0;
+    for (int row = 0; row < rm->rows; row++) {
+        for (int col = 0; col < rm->cols; col++) {
+            char cc = RMcharat(rm, col, row);
+            if ((cc == 'S') || (cc == '|')) {
+                char *pc = RMcharptr(rm, col, row+1);
+                if (pc == NULL) continue;
+                if (*pc == '.') {
+                    *pc = '|';
+                } else if (*pc == '^') {
+                    *(pc - 1) = *(pc + 1) = '|';
+                    count++;
+                } else if (*pc == '|') {
+                    /* do nothing */
+                } else {
+                    /* do nothing */
+                }
+            }
+        }
+    }
+    return count;
+}
+
+void aoc202507(char *data, size_t len) {
+    (void)len; // unused argument
+    struct RectangularMap rm[2] = {0};
+    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 (obviously!) and skip it
+    }
+    unsigned part1 = tachyon_splits(rm);
+    printf("P1: %u\n", part1);
+    RMfree(rm);
+    RMfree(rm + 1);
+}
 
 /* === aoc202506 =======================================================
 ===================================================================== */
 static long long unsigned add2506(long long unsigned v[4][1024], int lin, int col) {
     long long unsigned sum = 0;

Index: aocdailies.c
==================================================================
--- aocdailies.c
+++ aocdailies.c
@@ -4,10 +4,11 @@
 aocfunc *aocselect(unsigned y, unsigned d) {
     aocfunc *p;
     switch (y * 100 + d) {
         default: p = NULL; break;
 
+        case 202507: p = aoc202507; break;
         case 202506: p = aoc202506; break;
         case 202505: p = aoc202505; break;
         case 202504: p = aoc202504; break;
         case 202503: p = aoc202503; break;
         case 202502: p = aoc202502; break;

Index: aocdailies.h
==================================================================
--- aocdailies.h
+++ aocdailies.h
@@ -4,10 +4,11 @@
 #include <stddef.h>
 
 typedef void aocfunc(char *, size_t);
 aocfunc *aocselect(unsigned, unsigned);
 
+aocfunc aoc202507;
 aocfunc aoc202506;
 aocfunc aoc202505;
 aocfunc aoc202504;
 aocfunc aoc202503;
 aocfunc aoc202502;