diff --git a/src/c/day1.c b/src/c/day1.c
index cc9d7d5..16947c9 100644
--- a/src/c/day1.c
+++ b/src/c/day1.c
@@ -3,10 +3,15 @@
  *
  *  Grendel: a compiling Beowulf reimplementation.
  *
- *  Day 1 of work towards a compiler... eventually..
+ *  Day 1 of work towards a compiler... eventually...
  *
  *  This is a straight copy of Noah Zentzis' work. There's no original work of
- *  mine here, yet
+ *  mine here, yet.
+ *
+ *  See: https://generalproblem.net/lets_build_a_compiler/01-starting-out/
+ *
+ *  I needed to install (on Debian) the package `gcc-multilib` to get this to 
+ *  link.
  *
  *  (c) 2026 Simon Brooke <simon@journeyman.cc>
  *  Licensed under GPL version 2.0, or, at your option, any later version.
@@ -16,6 +21,12 @@
 #include <stdint.h>
 #include <string.h>
 
+/*
+ * "The `__attribute__((__cdecl__))` part is a GCC-specific syntax extension
+ * that tells the compiler to use the 
+ * "[cdecl](https://en.wikipedia.org/wiki/X86_calling_conventions#cdecl)" 
+ * calling convention when executing the function."
+ */
 __attribute__((__cdecl__))
 extern int lisp_entry();