diff --git a/src/board.h b/src/board.h
index 296b5de..c51fbdd 100644
--- a/src/board.h
+++ b/src/board.h
@@ -21,6 +21,7 @@
 typedef struct board_s {
     piece_t piece;
     piece_list_t *s_piece;
+    //struct list_head *s_piece;
 } board_t;                                        /* 0x88 board */
 #define BOARDSIZE    (8*8*2)
 
diff --git a/src/move.c b/src/move.c
index 290b98a..a2a7b58 100644
--- a/src/move.c
+++ b/src/move.c
@@ -147,10 +147,10 @@ static move_t *move_add(pos_t *pos, piece_t piece, square_t from,
           FILE2C(GET_F(to)),
           RANK2C(GET_R(to)));
 #   endif
-    /* impossible if opponent king is attacked
-     */
     if (COLOR(piece) != pos->turn)
         return NULL;
+    /* invalid position if opponent king is attacked
+     */
     if (board[to].piece & KING) {
 #       ifdef DEBUG_MOVE
         log_i(2, "invalid position: opponent king [%c%c] is in check.\n",
@@ -160,22 +160,20 @@ static move_t *move_add(pos_t *pos, piece_t piece, square_t from,
     }
     if (!(move = pool_get(moves_pool)))
         return NULL;
+    list_add(&move->list, &pos->moves);
 
     move->piece = piece;
     move->from = from;
     move->to = to;
     move->taken = board[to].piece;
     move->flags = M_NORMAL;
-    move->pos = NULL;
     if (move->taken)
         move->flags |= M_CAPTURE;
-    list_add(&move->list, &pos->moves);
+    move->newpos = pos_dup(pos);
 #   ifdef DEBUG_MOVE
     log_i(3, "added move from %c%c to %c%c\n",
-          FILE2C(GET_F(move->from)),
-          RANK2C(GET_R(move->from)),
-          FILE2C(GET_F(move->to)),
-          RANK2C(GET_R(move->to)));
+          FILE2C(GET_F(move->from)), RANK2C(GET_R(move->from)),
+          FILE2C(GET_F(move->to)), RANK2C(GET_R(move->to)));
 #   endif
     return move;
 }
@@ -191,8 +189,8 @@ void move_del(struct list_head *ptr)
 #   endif
 
     /* TODO: remove move->pos if non null */
-    if (move->pos) {
-        pos_clear(move->pos);
+    if (move->newpos) {
+        pos_clear(move->newpos);
     }
     list_del(ptr);
     pool_add(moves_pool, move);
@@ -223,6 +221,7 @@ static move_t *move_pawn_add(pos_t *pos, piece_t piece, square_t from,
     move_t *move;
     piece_t promote;
     unsigned char color = COLOR(piece);
+    pos_t *newpos;
 
     if (color != pos->turn)
         return NULL;
@@ -231,6 +230,8 @@ static move_t *move_pawn_add(pos_t *pos, piece_t piece, square_t from,
             if ((move = move_add(pos, piece, from, to))) {
                 move->flags |= M_PROMOTION;
                 move->promotion = promote | color;
+                newpos = move->newpos;
+                //piece_del(&newpos->board[from].s_piece);
             }
         }
     } else {
@@ -300,8 +301,10 @@ int pseudo_moves_pawn(pos_t *pos, piece_list_t *ppiece, bool doit)
 #               endif
                 //log_f(2, "pawn move2 mobility\n");
                 pos->mobility[vcolor]++;
-                if (doit && (move = move_pawn_add(pos, piece | color, square, new, rank7)))
+                if (doit &&
+                    (move = move_pawn_add(pos, piece | color, square, new, rank7))) {
                     count++;
+                }
             }
         }
     }
diff --git a/src/move.h b/src/move.h
index b769ce8..d539f8a 100644
--- a/src/move.h
+++ b/src/move.h
@@ -44,7 +44,7 @@ typedef struct move_s {
     piece_t promotion;                            /* promoted piece */
     move_flags_t flags;
     struct list_head list;                        /* next move */
-    struct pos_s *pos;                            /* resulting position */
+    struct pos_s *newpos;                         /* resulting position */
 } move_t;
 
 pool_t *moves_pool_init();
diff --git a/src/pool.c b/src/pool.c
index dab0714..30ae7af 100644
--- a/src/pool.c
+++ b/src/pool.c
@@ -117,7 +117,10 @@ void *pool_get(pool_t *pool)
         }
         pool_stats(pool);
     }
-    return  _pool_get(pool);
+    /* this is the effective address if the object (and also the
+     * pool list_head address)
+     */
+    return _pool_get(pool);
 }
 
 #ifdef BIN_pool
diff --git a/src/position.c b/src/position.c
index 9c3ed7b..4a526df 100644
--- a/src/position.c
+++ b/src/position.c
@@ -180,22 +180,32 @@ pos_t *pos_get()
 /* TODO: merge with pos_get - NULL for init, non null for duplicate */
 pos_t *pos_dup(pos_t *pos)
 {
+    struct list_head *p_cur, *tmp, *piece_list;
+    piece_list_t *oldpiece;
+    board_t *board;
     pos_t *new = pool_get(pos_pool);
-    if (new) {
-        //printf("sizeof(board)=%lu\n", sizeof (board_t));
-        //new->board = malloc(sizeof (board_t)*BOARDSIZE);
-        //if (!new->board) {
-        //    pool_add(pos_pool, new);
-        //    return NULL;
-        //}
 
+    if (new) {
+        board = new->board;
         *new = *pos;
         INIT_LIST_HEAD(&new->pieces[WHITE]);
         INIT_LIST_HEAD(&new->pieces[BLACK]);
         INIT_LIST_HEAD(&new->moves);
-        //printf("board mem: %p-%p\n", pos->board, pos->board+sizeof (board_t));
+
+        /* duplicate piece list */
+        for (int color=0; color<2; ++color) {
+            piece_list = &pos->pieces[color];     /* white/black piece list */
+
+            list_for_each_safe(p_cur, tmp, piece_list) {
+                oldpiece = list_entry(p_cur, piece_list_t, list);
+                board[oldpiece->square].s_piece =
+                    piece_add(new, oldpiece->piece, oldpiece->square);
+
+            }
+        }
+
     }
-    return pos;
+    return new;
 }
 
 pool_t *pos_pool_init()