diff --git a/src/arith/bignum.c b/src/arith/bignum.c
new file mode 100644
index 0000000..a21a7df
--- /dev/null
+++ b/src/arith/bignum.c
@@ -0,0 +1,14 @@
+/*
+ * bignum.c
+ *
+ * Allocation of and operations on arbitrary precision integers.
+ *
+ * (c) 2018 Simon Brooke <simon@journeyman.cc>
+ * Licensed under GPL version 2.0, or, at your option, any later version.
+ */
+
+/*
+ * Bignums generally follow Knuth, vol 2, 4.3. The word size is 64 bits,
+ * and words are stored in individual cons-space objects, comprising the
+ * word itself and a pointer to the next word in the number.
+ */
diff --git a/src/arith/bignum.h b/src/arith/bignum.h
new file mode 100644
index 0000000..05c9073
--- /dev/null
+++ b/src/arith/bignum.h
@@ -0,0 +1,16 @@
+/**
+ * bignum.h
+ *
+ * functions for bignum cells.
+ *
+ *
+ * (c) 2017 Simon Brooke <simon@journeyman.cc>
+ * Licensed under GPL version 2.0, or, at your option, any later version.
+ */
+
+#ifndef __bignum_h
+#define __bignum_h
+
+
+
+#endif
diff --git a/src/arith/integer.c b/src/arith/integer.c
index e069f52..60ce8c3 100644
--- a/src/arith/integer.c
+++ b/src/arith/integer.c
@@ -35,7 +35,7 @@ long double numeric_value( struct cons_pointer pointer ) {
 /**
  * Allocate an integer cell representing this value and return a cons pointer to it.
  */
-struct cons_pointer make_integer( long int value ) {
+struct cons_pointer make_integer( int64_t value ) {
     struct cons_pointer result = allocate_cell( INTEGERTAG );
     struct cons_space_object *cell = &pointer2cell( result );
     cell->payload.integer.value = value;
diff --git a/src/arith/integer.h b/src/arith/integer.h
index d44f34d..00b94a6 100644
--- a/src/arith/integer.h
+++ b/src/arith/integer.h
@@ -16,6 +16,6 @@ long double numeric_value( struct cons_pointer pointer );
 /**
  * Allocate an integer cell representing this value and return a cons pointer to it.
  */
-struct cons_pointer make_integer( long int value );
+struct cons_pointer make_integer( int64_t value );
 
 #endif
diff --git a/src/arith/peano.c b/src/arith/peano.c
index d43c768..2b0183d 100644
--- a/src/arith/peano.c
+++ b/src/arith/peano.c
@@ -27,7 +27,7 @@
 #include "stack.h"
 
 long double to_long_double( struct cons_pointer arg );
-long int to_long_int( struct cons_pointer arg );
+int64_t to_long_int( struct cons_pointer arg );
 struct cons_pointer add_2( struct stack_frame *frame, struct cons_pointer arg1,
                            struct cons_pointer arg2 );
 
@@ -97,8 +97,8 @@ long double to_long_double( struct cons_pointer arg ) {
  * if a ratio may legally have zero as a divisor, or something which is
  * not a number (or is a big number) is passed in.
  */
-long int to_long_int( struct cons_pointer arg ) {
-    long int result = 0;
+int64_t to_long_int( struct cons_pointer arg ) {
+    int64_t result = 0;
     struct cons_space_object cell = pointer2cell( arg );
     switch ( cell.tag.value ) {
         case INTEGERTV:
@@ -125,10 +125,13 @@ struct cons_pointer add_2( struct stack_frame *frame, struct cons_pointer arg1,
     struct cons_space_object cell1 = pointer2cell( arg1 );
     struct cons_space_object cell2 = pointer2cell( arg2 );
 
+#ifdef DEBUG
     fputws( L"add_2( arg1 = ", stderr );
     print( stderr, arg1 );
     fputws( L"; arg2 = ", stderr );
     print( stderr, arg2 );
+    fputws( L")\n", stderr);
+#endif
 
     if ( zerop( arg1 ) ) {
         result = arg2;
@@ -199,9 +202,11 @@ struct cons_pointer add_2( struct stack_frame *frame, struct cons_pointer arg1,
         }
     }
 
+#ifdef DEBUG
     fputws( L"}; => ", stderr );
     print( stderr, arg2 );
     fputws( L"\n", stderr );
+#endif
 
     return result;
 }
@@ -254,17 +259,19 @@ struct cons_pointer multiply_2( struct stack_frame *frame,
     struct cons_space_object cell1 = pointer2cell( arg1 );
     struct cons_space_object cell2 = pointer2cell( arg2 );
 
+#ifdef DEBUG
     fputws( L"multiply_2( arg1 = ", stderr );
     print( stderr, arg1 );
     fputws( L"; arg2 = ", stderr );
     print( stderr, arg2 );
+    fputws( L")\n", stderr);
+#endif
 
     if ( zerop( arg1 ) ) {
         result = arg2;
     } else if ( zerop( arg2 ) ) {
         result = arg1;
     } else {
-
         switch ( cell1.tag.value ) {
             case EXCEPTIONTV:
                 result = arg1;
@@ -328,9 +335,11 @@ struct cons_pointer multiply_2( struct stack_frame *frame,
         }
     }
 
-    fputws( L"}; => ", stderr );
+#ifdef DEBUG
+    fputws( L" => ", stderr );
     print( stderr, arg2 );
     fputws( L"\n", stderr );
+#endif
 
     return result;
 }
diff --git a/src/arith/ratio.c b/src/arith/ratio.c
index 28ba59a..ff716ec 100644
--- a/src/arith/ratio.c
+++ b/src/arith/ratio.c
@@ -28,9 +28,9 @@ struct cons_pointer inverse( struct stack_frame *frame,
                              struct cons_pointer arg );
 
 /**
- * return, as a long int, the greatest common divisor of `m` and `n`,
+ * return, as a int64_t, the greatest common divisor of `m` and `n`,
  */
-long int greatest_common_divisor( long int m, long int n ) {
+int64_t greatest_common_divisor( int64_t m, int64_t n ) {
     int o;
     while ( m ) {
         o = m;
@@ -42,9 +42,9 @@ long int greatest_common_divisor( long int m, long int n ) {
 }
 
 /**
- * return, as a long int, the least common multiple of `m` and `n`,
+ * return, as a int64_t, the least common multiple of `m` and `n`,
  */
-long int least_common_multiple( long int m, long int n ) {
+int64_t least_common_multiple( int64_t m, int64_t n ) {
     return m / greatest_common_divisor( m, n ) * n;
 }
 
@@ -59,7 +59,7 @@ struct cons_pointer simplify_ratio( struct stack_frame *frame,
     struct cons_pointer result = arg;
 
   if (ratiop(arg)) {
-    long int ddrv =
+    int64_t ddrv =
         pointer2cell( pointer2cell( arg ).payload.ratio.dividend ).
         payload.integer.value, drrv =
         pointer2cell( pointer2cell( arg ).payload.ratio.divisor ).
@@ -106,7 +106,7 @@ struct cons_pointer add_ratio_ratio( struct stack_frame *frame,
   if ( ratiop(arg1) && ratiop(arg2)) {
     struct cons_space_object cell1 = pointer2cell( arg1 );
     struct cons_space_object cell2 = pointer2cell( arg2 );
-    long int dd1v =
+    int64_t dd1v =
         pointer2cell( cell1.payload.ratio.dividend ).payload.integer.value,
         dd2v =
         pointer2cell( cell2.payload.ratio.dividend ).payload.integer.value,
@@ -231,7 +231,7 @@ struct cons_pointer multiply_ratio_ratio( struct
   if ( ratiop(arg1) && ratiop(arg2)) {
     struct cons_space_object cell1 = pointer2cell( arg1 );
     struct cons_space_object cell2 = pointer2cell( arg2 );
-    long int dd1v =
+    int64_t dd1v =
         pointer2cell( cell1.payload.ratio.dividend ).payload.integer.value,
         dd2v =
         pointer2cell( cell2.payload.ratio.dividend ).payload.integer.value,
diff --git a/src/memory/conspage.c b/src/memory/conspage.c
index c5920c0..13d8373 100644
--- a/src/memory/conspage.c
+++ b/src/memory/conspage.c
@@ -127,8 +127,10 @@ void dump_pages( FILE * output ) {
 void free_cell( struct cons_pointer pointer ) {
     struct cons_space_object *cell = &pointer2cell( pointer );
 
+#ifdef DEBUG
     fwprintf( stderr, L"Freeing cell " );
     dump_object( stderr, pointer );
+#endif
 
     switch ( cell->tag.value ) {
             /* for all the types of cons-space object which point to other
@@ -173,7 +175,7 @@ void free_cell( struct cons_pointer pointer ) {
 
     if ( !check_tag( pointer, FREETAG ) ) {
         if ( cell->count == 0 ) {
-            strncpy( &cell->tag.bytes[0], FREETAG, 4 );
+            strncpy( &cell->tag.bytes[0], FREETAG, TAGLENGTH );
             cell->payload.free.car = NIL;
             cell->payload.free.cdr = freelist;
             freelist = pointer;
@@ -209,7 +211,7 @@ struct cons_pointer allocate_cell( char *tag ) {
         if ( strncmp( &cell->tag.bytes[0], FREETAG, TAGLENGTH ) == 0 ) {
             freelist = cell->payload.free.cdr;
 
-            strncpy( &cell->tag.bytes[0], tag, 4 );
+            strncpy( &cell->tag.bytes[0], tag, TAGLENGTH );
 
             cell->count = 0;
             cell->payload.cons.car = NIL;
diff --git a/src/memory/consspaceobject.h b/src/memory/consspaceobject.h
index 50ad5e1..555614a 100644
--- a/src/memory/consspaceobject.h
+++ b/src/memory/consspaceobject.h
@@ -28,6 +28,13 @@
 /**
  * tag values, all of which must be 4 bytes. Must not collide with vector space tag values
  */
+
+/**
+ * A word within a bignum - arbitrary precision integer.
+ */
+#define BIGNUMTAG "BIGN"
+#define BIGNUMTV 1313294658
+
 /**
  * An ordinary cons cell: 1397641027
  */
@@ -38,7 +45,6 @@
  * An exception.
  */
 #define EXCEPTIONTAG "EXEP"
-/* TODO: this is wrong */
 #define EXCEPTIONTV 1346721861
 
 /**
@@ -162,6 +168,11 @@
  */
 #define nilp(conspoint) (check_tag(conspoint,NILTAG))
 
+/**
+ * true if conspointer points to a cons cell, else false
+ */
+#define bignump(conspoint) (check_tag(conspoint,BIGNUMTAG))
+
 /**
  * true if conspointer points to a cons cell, else false
  */
@@ -221,7 +232,7 @@
  * true if conspointer points to some sort of a number cell,
  * else false
  */
-#define numberp(conspoint) (check_tag(conspoint,INTEGERTAG)||check_tag(conspoint,RATIOTAG)||heck_tag(conspoint,REALTAG))
+#define numberp(conspoint) (check_tag(conspoint,INTEGERTAG)||check_tag(conspoint,RATIOTAG)||check_tag(conspoint,REALTAG)||check_tag(conspoint,BIGNUMTAG))
 
 /**
  * true if thr conspointer points to a vector pointer.
@@ -274,6 +285,16 @@ struct stack_frame {
     struct cons_pointer function; /* the function to be called */
 };
 
+/**
+ * payload of a bignum cell. Intentionally similar to an integer payload, but
+ * with a next pointer.
+ */
+struct bignum_payload {
+    int64_t value;
+    struct cons_pointer next;
+};
+
+
 /**
  * payload of a cons cell.
  */
@@ -321,7 +342,7 @@ struct free_payload {
  * optional bignum object.
  */
 struct integer_payload {
-    long int value;
+    int64_t value;
 };
 
 /**
diff --git a/src/memory/vectorspace.c b/src/memory/vectorspace.c
index 6e331d6..4b18b96 100644
--- a/src/memory/vectorspace.c
+++ b/src/memory/vectorspace.c
@@ -45,9 +45,9 @@ struct cons_pointer make_vec_pointer( char *tag, uint64_t address ) {
  * NOTE that `tag` should be the vector-space tag of the particular type of
  * vector-space object, NOT `VECTORPOINTTAG`.
  */
-struct cons_pointer make_vso( char *tag, long int payload_size ) {
+struct cons_pointer make_vso( char *tag, int64_t payload_size ) {
     struct cons_pointer result = NIL;
-    long int total_size = sizeof( struct vector_space_header ) + payload_size;
+    int64_t total_size = sizeof( struct vector_space_header ) + payload_size;
 
     struct vector_space_header *vso = malloc( total_size );
 
diff --git a/src/memory/vectorspace.h b/src/memory/vectorspace.h
index b338766..07a0b91 100644
--- a/src/memory/vectorspace.h
+++ b/src/memory/vectorspace.h
@@ -34,6 +34,11 @@
 #define NAMESPACETAG "NMSP"
 #define NAMESPACETV 0
 
+/*
+ * a stack frame.
+ */
+#define STACKFRAMETAG "STAK"
+#define STACKFRAMETV
 /*
  * a vector of cons pointers.
  */
@@ -42,7 +47,7 @@
 
 #define pointer_to_vso(pointer)(vectorpointp(pointer)? pointer2cell(pointer).payload.vectorp.address : 0)
 
-struct cons_pointer make_vso( char *tag, long int payload_size );
+struct cons_pointer make_vso( char *tag, int64_t payload_size );
 
 struct vector_space_header {
     union {
diff --git a/src/ops/read.c b/src/ops/read.c
index e5a41a5..9c21c9a 100644
--- a/src/ops/read.c
+++ b/src/ops/read.c
@@ -125,8 +125,8 @@ struct cons_pointer read_continuation( struct stack_frame *frame, FILE * input,
 struct cons_pointer read_number( struct stack_frame *frame, FILE * input,
                                  wint_t initial, bool seen_period ) {
     struct cons_pointer result = NIL;
-    long int accumulator = 0;
-    long int dividend = 0;
+    int64_t accumulator = 0;
+    int64_t dividend = 0;
     int places_of_decimals = 0;
     wint_t c;
     fwprintf( stderr, L"read_number starting '%c' (%d)\n", initial, initial );
diff --git a/utils_src/tagvalcalc/tagvalcalc.c b/utils_src/tagvalcalc/tagvalcalc.c
index 1159187..67828bd 100644
--- a/utils_src/tagvalcalc/tagvalcalc.c
+++ b/utils_src/tagvalcalc/tagvalcalc.c
@@ -1,9 +1,26 @@
 #include <stdint.h>
 #include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define TAGLENGTH 4
+
+struct dummy {
+  union {
+    char bytes[TAGLENGTH];  /* the tag (type) of this cell,
+                                   * considered as bytes */
+    uint32_t value;         /* the tag considered as a number */
+  } tag;
+};
 
 int main( int argc, char *argv[] ) {
+  struct dummy *b = malloc( sizeof( struct dummy));
+  struct dummy buffer = *b;
 
   for (int i = 1; i < argc; i++) {
-    printf( "%4.4s:\t%u\n", argv[i], (uint32_t)*argv[i]);
+
+    strncpy( &buffer.tag.bytes[0], argv[i], TAGLENGTH );
+
+    printf( "%4.4s:\t%d\n", argv[i], buffer.tag.value);
   }
 }
diff --git a/utils_src/tagvalcalc/tvc b/utils_src/tagvalcalc/tvc
index 8fb6cb3..a639364 100755
Binary files a/utils_src/tagvalcalc/tvc and b/utils_src/tagvalcalc/tvc differ