Lots more code written, and I think most of it's OK; but it doesn't compile yet.

src/c/ops/eq.c

@@ -0,0 +1,56 @@
+/**
+ *  ops/eq.c
+ *
+ *  Post Scarcity Software Environment: eq.
+ *
+ *  Test for pointer equality.
+ *
+ *  (c) 2026 Simon Brooke <simon@journeyman.cc>
+ *  Licensed under GPL version 2.0, or, at your option, any later version.
+ */
+
+#include "memory/memory.h"
+#include "memory/pointer.h"
+#include "memory/stack.h"
+
+/**
+ * @brief Function; do these two pointers point to the same object? 
+ *
+ * Shallow, cheap equality.
+ *
+ * TODO: if either of these pointers points to a cache cell, then what
+ * we need to check is the cached value, which is not so cheap. Ouch!
+ *
+ * @param a a pointer;
+ * @param b another pointer;
+ * @return `true` if they are the same, else `false`
+ */
+bool eq( struct pso_pointer a, struct pso_pointer b) {
+    return ( a.node == b.node && a.page == b.page && a.offset == b.offset);
+}
+
+/**
+ * Function; do all arguments to this finction point to the same object? 
+ *
+ * Shallow, cheap equality.
+ *
+ * * (eq? args...)
+ *
+ * @param frame my stack_frame.
+ * @param frame_pointer a pointer to my stack_frame.
+ * @param env my environment (ignored).
+ * @return `t` if all args are pointers to the same object, else `nil`;
+ */
+struct pso_pointer lisp_eq( struct stack_frame *frame,
+                             struct pso_pointer frame_pointer,
+                             struct pso_pointer env ) {
+    struct pso_pointer result = t;
+
+    if ( frame->args > 1 ) {
+        for ( int b = 1; ( truep( result ) ) && ( b < frame->args ); b++ ) {
+            result = eq( frame->arg[0], fetch_arg( frame, b ) ) ? t : nil;
+        }
+    }
+
+    return result;
+}