diff --git a/multi_process_infer_by_pairs.py b/functions/multi_process_infer_by_pairs.py
similarity index 90%
rename from multi_process_infer_by_pairs.py
rename to functions/multi_process_infer_by_pairs.py
index 911b402..199d4ef 100644
--- a/multi_process_infer_by_pairs.py
+++ b/functions/multi_process_infer_by_pairs.py
@@ -6,13 +6,18 @@ import copy
 
 conf_thresh = 0.8
 
+
 def my_Levenshtein_ratio(str1, str2):
+    if max(len(str1), len(str2)) == 0:
+        return 1
     return 1 - Levenshtein.distance(str1, str2) / max(len(str1), len(str2))
 
 
 def if_minimal(md, md_list, target_col):
     # 假设这个md是minimal
     minimal = True
+    if md_list.count(md) > 1:
+        return False
     for _ in md_list:
         if _ != md:
             # 假设列表中每一个md都使当前md不minimal
@@ -48,6 +53,7 @@ def remove_by_confidence(md, l, relation, target_col, lock):
 
 def inference_from_record_pairs(path, threshold, target_col):
     data = pd.read_csv(path, low_memory=False, encoding='ISO-8859-1')
+    data.fillna("", inplace=True)
     data = data.astype(str)
     columns = data.columns.values.tolist()
 
@@ -71,7 +77,8 @@ def inference_from_record_pairs(path, threshold, target_col):
                 sims[col] = similarity
 
             # 寻找violated md,从md列表中删除并加入vio列表
-            for md in md_list:
+            # tmp_md_list = copy.deepcopy(md_list)
+            for md in md_list[:]:
                 lhs_satis = True
                 rhs_satis = True
                 for col in list(set(columns) - {target_col}):
@@ -101,33 +108,39 @@ def inference_from_record_pairs(path, threshold, target_col):
                         if if_minimal(spec_l_md, md_list, target_col):
                             md_list.append(spec_l_md)
 
-            for vio in minimal_vio:
+            # tmp_minimal_vio = copy.deepcopy(minimal_vio)
+            for vio in minimal_vio[:]:
                 if not if_minimal(vio, md_list, target_col):
                     minimal_vio.remove(vio)
 
     manager = multiprocessing.Manager()
     lock = manager.Lock()
     if len(minimal_vio) == 0:
-        return [], []
+        return md_list, []
     pool = multiprocessing.Pool(len(minimal_vio))
-    tmp = copy.deepcopy(minimal_vio)
+    # tmp = copy.deepcopy(minimal_vio)
     with manager:
         proxy_minimal_vio = manager.list(minimal_vio)
-        for _ in tmp:
+        for _ in minimal_vio[:]:
             pool.apply_async(remove_by_confidence, args=(_, proxy_minimal_vio, data, target_col, lock))
         pool.close()
         pool.join()
         minimal_vio = list(proxy_minimal_vio)
 
-    for _ in tmp:
+    for _ in minimal_vio[:]:
         if not if_minimal(_, minimal_vio, target_col):
             minimal_vio.remove(_)
 
+    for _ in md_list[:]:
+        if not if_minimal(_, md_list, target_col):
+            md_list.remove(_)
+
     return md_list, minimal_vio
 
 
 def get_mds_metadata(md_list, dataset_path, target_col):
     data = pd.read_csv(dataset_path, low_memory=False, encoding='ISO-8859-1')
+    data.fillna("", inplace=True)
     data = data.astype(str)
 
     manager = multiprocessing.Manager()