diff --git a/src/io/read.c b/src/io/read.c
index bf92f35..50f469e 100644
--- a/src/io/read.c
+++ b/src/io/read.c
@@ -32,6 +32,16 @@
 #include "arith/real.h"
 #include "memory/vectorspace.h"
 
+// We can't, I think, use libreadline, because we read character by character, 
+// not line by line, and because we use wide characters. So we're going to have
+// to reimplement it. So we're going to have to maintain history of the forms
+// (or strings, but I currently think forms). So we're going to have to be able
+// to detact special keys, particularly, at this stage, the uparrow and down-
+// arrow keys
+// #include <readline/readline.h>
+// #include <readline/history.h>
+
+
 /*
  * for the time being things which may be read are: 
  * * strings
@@ -325,11 +335,10 @@ struct cons_pointer read_number( struct stack_frame *frame,
                 }
                 break;
             case LCOMMA:
-                // silently ignore it.
+                // silently ignore comma.
                 break;
             default:
                 result = add_integers( multiply_integers( result, base ),
-                                        /* /todo: this won't work for hex digits */
                                        make_integer( ( int ) c - ( int ) '0',
                                                      NIL ) );
 
diff --git a/src/memory/consspaceobject.h b/src/memory/consspaceobject.h
index e9a75a6..609226d 100644
--- a/src/memory/consspaceobject.h
+++ b/src/memory/consspaceobject.h
@@ -121,6 +121,30 @@
  */
 #define LOOPTV     1347374924
 
+/**
+ * @brief Tag for a lazy cons cell.
+ * 
+ * A lazy cons cell is like a cons cell, but lazy.
+ * 
+ */
+#define LAZYCONSTAG "LZYC"
+
+/**
+ * @brief Tag for a lazy string cell.
+ * 
+ * A lazy string cell is like a string cell, but lazy.
+ * 
+ */
+#define LAZYSTRTAG "LZYS"
+
+/**
+ * @brief Tag for a lazy worker cell.
+ * 
+ * A lazy 
+ * 
+ */
+#define LAZYWRKRTAG "WRKR"
+
 /**
  * The special cons cell at address {0,0} whose car and cdr both point to
  * itself.
diff --git a/unit-tests/bignum-add.sh b/unit-tests/bignum-add.sh
index 7bbb41e..778015a 100755
--- a/unit-tests/bignum-add.sh
+++ b/unit-tests/bignum-add.sh
@@ -129,6 +129,51 @@ else
 fi
 
 
+#####################################################################
+# add two small bignums to produce a bigger bignum
+
+a=1152921504606846977
+c=`echo "$a + $a" | bc`
+echo -n "adding $a to $a: "
+expected='t'
+output=`echo "(= (+ $a $b) $c)" | target/psse -v 2 2>psse.log`
+
+actual=`echo $output |\
+  tail -1 |\
+  sed 's/\,//g'`
+
+if [ "${expected}" = "${actual}" ]
+then
+    echo "OK"
+else
+    echo "Fail: expected '${expected}', got '${actual}'"
+    exit 1
+fi
+
+#####################################################################
+# add five small bignums to produce a bigger bignum
+
+a=1152921504606846977
+c=`echo "$a * 5" | bc`
+echo -n "adding $a, $a $a, $a, $a: "
+expected='t'
+output=`echo "(= (+ $a $a $a $a $a) $c)" | target/psse -v 2 2>psse.log`
+
+actual=`echo $output |\
+  tail -1 |\
+  sed 's/\,//g'`
+
+if [ "${expected}" = "${actual}" ]
+then
+    echo "OK"
+else
+    echo "Fail: expected '${expected}', got '${actual}'"
+    exit 1
+fi
+
+
+
+
 #####################################################################
 # add two bignums to produce a bignum
 a=10000000000000000000