diff --git a/mu-init.subx b/mu-init.subx
index 08a8856e..b60249ba 100644
--- a/mu-init.subx
+++ b/mu-init.subx
@@ -12,6 +12,7 @@
 Entry:
   # initialize stack
   bd/copy-to-ebp 0/imm32
+#?   (main 0 0 Primary-bus-secondary-drive)
   # always first run tests
   (run-tests)
   (num-test-failures)  # => eax
diff --git a/shell/cell.mu b/shell/cell.mu
index 8c4db86f..1aed590d 100644
--- a/shell/cell.mu
+++ b/shell/cell.mu
@@ -90,6 +90,10 @@ fn new-pair out: (addr handle cell), left: (handle cell), right: (handle cell) {
   initialize-pair out, left, right
 }
 
+fn nil out: (addr handle cell) {
+  allocate-pair out
+}
+
 fn allocate-primitive-function _out: (addr handle cell) {
   var out/eax: (addr handle cell) <- copy _out
   allocate out
diff --git a/shell/evaluate.mu b/shell/evaluate.mu
index 00a75b9a..19fe9fdc 100644
--- a/shell/evaluate.mu
+++ b/shell/evaluate.mu
@@ -10,7 +10,7 @@ fn evaluate _in: (addr handle cell), out: (addr handle cell), env-h: (handle cel
 #?   }
   # trace "evaluate " in " in environment " env {{{
   {
-    var stream-storage: (stream byte 0x40)
+    var stream-storage: (stream byte 0x100)
     var stream/ecx: (addr stream byte) <- address stream-storage
     write stream, "evaluate "
     print-cell in, stream, 0/no-trace
@@ -232,7 +232,7 @@ fn apply _f-ah: (addr handle cell), args-ah: (addr handle cell), out: (addr hand
   # if it's not a primitive function it must be an anonymous function
   # trace "apply anonymous function " f " in environment " env {{{
   {
-    var stream-storage: (stream byte 0x40)
+    var stream-storage: (stream byte 0x100)
     var stream/ecx: (addr stream byte) <- address stream-storage
     write stream, "apply anonymous function "
     print-cell _f-ah, stream, 0/no-trace
@@ -318,7 +318,7 @@ fn push-bindings _params-ah: (addr handle cell), _args-ah: (addr handle cell), o
   # Params can only be symbols or pairs. Args can be anything.
   # trace "pushing bindings from " params " to " args {{{
   {
-    var stream-storage: (stream byte 0x40)
+    var stream-storage: (stream byte 0x100)
     var stream/ecx: (addr stream byte) <- address stream-storage
     write stream, "pushing bindings from "
     print-cell params-ah, stream, 0/no-trace
diff --git a/shell/global.mu b/shell/global.mu
index 107d85e7..5d34298b 100644
--- a/shell/global.mu
+++ b/shell/global.mu
@@ -20,6 +20,7 @@ fn initialize-globals _self: (addr global-table) {
   append-primitive self, "car"
   append-primitive self, "cdr"
   append-primitive self, "cons"
+  append-primitive self, "="
 }
 
 fn render-globals screen: (addr screen), _self: (addr global-table), xmin: int, ymin: int, xmax: int, ymax: int {
@@ -237,6 +238,13 @@ fn apply-primitive _f: (addr cell), args-ah: (addr handle cell), out: (addr hand
     apply-cons args-ah, out, env-h, trace
     return
   }
+  {
+    var is-compare?/eax: boolean <- string-equal? f-name, "="
+    compare is-compare?, 0/false
+    break-if-=
+    apply-compare args-ah, out, env-h, trace
+    return
+  }
   abort "unknown primitive function"
 }
 
@@ -542,3 +550,39 @@ fn apply-cons _args-ah: (addr handle cell), out: (addr handle cell), env-h: (han
   # cons
   new-pair out, *first-ah, *second-ah
 }
+
+fn apply-compare _args-ah: (addr handle cell), out: (addr handle cell), env-h: (handle cell), trace: (addr trace) {
+  trace-text trace, "eval", "apply ="
+  var args-ah/eax: (addr handle cell) <- copy _args-ah
+  var _args/eax: (addr cell) <- lookup *args-ah
+  var args/esi: (addr cell) <- copy _args
+  var _env/eax: (addr cell) <- lookup env-h
+  var env/edi: (addr cell) <- copy _env
+  # TODO: check that args is a pair
+  var empty-args?/eax: boolean <- nil? args
+  compare empty-args?, 0/false
+  {
+    break-if-=
+    error trace, "cons needs 2 args but got 0"
+    return
+  }
+  # args->left
+  var first-ah/ecx: (addr handle cell) <- get args, left
+  # args->right->left
+  var right-ah/eax: (addr handle cell) <- get args, right
+  var right/eax: (addr cell) <- lookup *right-ah
+  # TODO: check that right is a pair
+  var second-ah/edx: (addr handle cell) <- get right, left
+  # compare
+  var _first/eax: (addr cell) <- lookup *first-ah
+  var first/ecx: (addr cell) <- copy _first
+  var second/eax: (addr cell) <- lookup *second-ah
+  var match?/eax: boolean <- cell-isomorphic? first, second, trace
+  compare match?, 0/false
+  {
+    break-if-!=
+    nil out
+    return
+  }
+  new-integer out, 1/true
+}