diff --git a/mmapcp.cc b/mmapcp.cc
index c18496c..2807110 100644
--- a/mmapcp.cc
+++ b/mmapcp.cc
@@ -10,23 +10,30 @@ int main (int argc, char *argv[]) {
   struct stat st, s2t;
   int s = open(argv[1], O_RDONLY);
   if (s == -1) { perror("open source"); exit(1); }
+
   int s2 = open(argv[2], O_RDONLY);
   if (s2 == -1) { perror("open source2"); exit(1); }
+
   if (open(argv[3], O_RDONLY) > 0) { perror("destination file exists. abort. open destfile"); exit(1); }
   int d = open(argv[3], O_RDWR | O_CREAT, 0644);
   if (d == -1) { perror("open destination"); exit(1); }
+
   if (fstat(s, &st)) { perror("stat source"); exit(1); }
   if (fstat(s2, &s2t)) { perror("stat source2"); exit(1); }
   if (ftruncate(d, st.st_size + s2t.st_size)) { perror("truncate destination"); exit(1); }
+
   void *sp = mmap(NULL, st.st_size, PROT_READ, MAP_SHARED, s, 0);
   if (sp == MAP_FAILED) { perror("map source"); exit(1); }
   madvise(sp, st.st_size, MADV_SEQUENTIAL);
+
   void *s2p = mmap(NULL, s2t.st_size, PROT_READ, MAP_SHARED, s2, 0);
   if (s2p == MAP_FAILED) { perror("map source2"); exit(1); }
   madvise(s2p, s2t.st_size, MADV_SEQUENTIAL);
+
   void *dp = mmap(NULL, st.st_size + s2t.st_size, PROT_WRITE | PROT_READ, MAP_SHARED, d, 0);
   if (dp == MAP_FAILED) { perror("map destination"); exit(1); }
   madvise(dp, st.st_size + s2t.st_size, MADV_SEQUENTIAL);
+
   memcpy(mempcpy(dp, sp, st.st_size), s2p, s2t.st_size);
   return 0;
 }