diff --git a/srfi/srfi-1.c b/srfi/srfi-1.c
index 02f46fc..268f1dc 100644
--- a/srfi/srfi-1.c
+++ b/srfi/srfi-1.c
@@ -211,7 +211,7 @@ SCM_DEFINE (scm_srfi1_break, "break", 2, 0, 0,
   for ( ; scm_is_pair (lst); lst = SCM_CDR (lst))
     {
       SCM elem = SCM_CAR (lst);
-      if (scm_is_true (pred_tramp (pred, elem)))
+      if (scm_is_true_and_not_lisp_nil (pred_tramp (pred, elem)))
         goto done;
 
       /* want this elem, tack it onto the end of ret */
@@ -243,7 +243,7 @@ SCM_DEFINE (scm_srfi1_break_x, "break!", 2, 0, 0,
   p = &lst;
   for (upto = lst; scm_is_pair (upto); upto = SCM_CDR (upto))
     {
-      if (scm_is_true (pred_tramp (pred, SCM_CAR (upto))))
+      if (scm_is_true_and_not_lisp_nil (pred_tramp (pred, SCM_CAR (upto))))
         goto done;
 
       /* want this element */
@@ -334,7 +334,8 @@ SCM_DEFINE (scm_srfi1_count, "count", 2, 0, 1,
       SCM_ASSERT (pred_tramp, pred, SCM_ARG1, FUNC_NAME);
 
       for ( ; scm_is_pair (list1); list1 = SCM_CDR (list1))
-        count += scm_is_true (pred_tramp (pred, SCM_CAR (list1)));
+        count += scm_is_true_and_not_lisp_nil (pred_tramp (pred,
+							   SCM_CAR (list1)));
 
       /* check below that list1 is a proper list, and done */
     end_list1:
@@ -361,8 +362,9 @@ SCM_DEFINE (scm_srfi1_count, "count", 2, 0, 1,
               argnum = 3;
               break;
             }
-          count += scm_is_true (pred_tramp
-				(pred, SCM_CAR (list1), SCM_CAR (list2)));
+          count += scm_is_true_and_not_lisp_nil (pred_tramp
+						 (pred, SCM_CAR (list1),
+						  SCM_CAR (list2)));
           list1 = SCM_CDR (list1);
           list2 = SCM_CDR (list2);
         }
@@ -396,7 +398,8 @@ SCM_DEFINE (scm_srfi1_count, "count", 2, 0, 1,
               SCM_SIMPLE_VECTOR_SET (vec, i, SCM_CDR (lst));  /* rest of lst */
             }
 
-          count += scm_is_true (scm_apply (pred, args, SCM_EOL));
+          count += scm_is_true_and_not_lisp_nil (scm_apply (pred, args,
+							    SCM_EOL));
         }
     }
 
@@ -452,7 +455,7 @@ SCM_DEFINE (scm_srfi1_delete, "delete", 2, 1, 0,
 
   for ( ; scm_is_pair (lst); lst = SCM_CDR (lst))
     {
-      if (scm_is_true (equal_p (pred, x, SCM_CAR (lst))))
+      if (scm_is_true_and_not_lisp_nil (equal_p (pred, x, SCM_CAR (lst))))
         {
           /* delete this element, so copy those at keeplst */
           p = list_copy_part (keeplst, count, p);
@@ -509,7 +512,7 @@ SCM_DEFINE (scm_srfi1_delete_x, "delete!", 2, 1, 0,
        scm_is_pair (walk);
        walk = SCM_CDR (walk))
     {
-      if (scm_is_true (equal_p (pred, x, SCM_CAR (walk))))
+      if (scm_is_true_and_not_lisp_nil (equal_p (pred, x, SCM_CAR (walk))))
 	*prev = SCM_CDR (walk);
       else
 	prev = SCM_CDRLOC (walk);
@@ -591,7 +594,7 @@ SCM_DEFINE (scm_srfi1_delete_duplicates, "delete-duplicates", 1, 1, 0,
       /* look for item in "ret" list */
       for (l = ret; scm_is_pair (l); l = SCM_CDR (l))
         {
-          if (scm_is_true (equal_p (pred, SCM_CAR (l), item)))
+          if (scm_is_true_and_not_lisp_nil (equal_p (pred, SCM_CAR (l), item)))
             {
               /* "item" is a duplicate, so copy keeplst onto ret */
             duplicate:
@@ -608,7 +611,7 @@ SCM_DEFINE (scm_srfi1_delete_duplicates, "delete-duplicates", 1, 1, 0,
       for (i = 0,       l = keeplst;
            i < count && scm_is_pair (l);
            i++,         l = SCM_CDR (l))
-        if (scm_is_true (equal_p (pred, SCM_CAR (l), item)))
+        if (scm_is_true_and_not_lisp_nil (equal_p (pred, SCM_CAR (l), item)))
           goto duplicate;
 
       /* keep this element */
@@ -684,7 +687,8 @@ SCM_DEFINE (scm_srfi1_delete_duplicates_x, "delete-duplicates!", 1, 1, 0,
           l = ret;
           for (;;)
             {
-              if (scm_is_true (equal_p (pred, SCM_CAR (l), item)))
+              if (scm_is_true_and_not_lisp_nil (equal_p (pred, SCM_CAR (l),
+							 item)))
                 break;  /* equal, forget this element */
 
               if (scm_is_eq (l, endret))
@@ -770,7 +774,7 @@ SCM_DEFINE (scm_srfi1_drop_while, "drop-while", 2, 0, 0,
   SCM_ASSERT (pred_tramp, pred, SCM_ARG1, FUNC_NAME);
 
   for ( ; scm_is_pair (lst); lst = SCM_CDR (lst))
-    if (scm_is_false (pred_tramp (pred, SCM_CAR (lst))))
+    if (scm_is_false_or_lisp_nil (pred_tramp (pred, SCM_CAR (lst))))
       goto done;
 
   SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (lst), lst, SCM_ARG2, FUNC_NAME, "list");
@@ -824,7 +828,7 @@ SCM_DEFINE (scm_srfi1_filter_map, "filter-map", 2, 0, 1,
       for ( ; scm_is_pair (list1); list1 = SCM_CDR (list1))
         {
           elem = proc_tramp (proc, SCM_CAR (list1));
-          if (scm_is_true (elem))
+          if (scm_is_true_and_not_lisp_nil (elem))
             {
               newcell = scm_cons (elem, SCM_EOL);
               *loc = newcell;
@@ -855,7 +859,7 @@ SCM_DEFINE (scm_srfi1_filter_map, "filter-map", 2, 0, 1,
               goto check_lst_and_done;
             }
           elem = proc_tramp (proc, SCM_CAR (list1), SCM_CAR (list2));
-          if (scm_is_true (elem))
+          if (scm_is_true_and_not_lisp_nil (elem))
             {
               newcell = scm_cons (elem, SCM_EOL);
               *loc = newcell;
@@ -895,7 +899,7 @@ SCM_DEFINE (scm_srfi1_filter_map, "filter-map", 2, 0, 1,
             }
 
           elem = scm_apply (proc, args, SCM_EOL);
-          if (scm_is_true (elem))
+          if (scm_is_true_and_not_lisp_nil (elem))
             {
               newcell = scm_cons (elem, SCM_EOL);
               *loc = newcell;
@@ -924,7 +928,7 @@ SCM_DEFINE (scm_srfi1_find, "find", 2, 0, 0,
   for ( ; scm_is_pair (lst); lst = SCM_CDR (lst))
     {
       SCM elem = SCM_CAR (lst);
-      if (scm_is_true (pred_tramp (pred, elem)))
+      if (scm_is_true_and_not_lisp_nil (pred_tramp (pred, elem)))
         return elem;
     }
   SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (lst), lst, SCM_ARG2, FUNC_NAME, "list");
@@ -945,7 +949,7 @@ SCM_DEFINE (scm_srfi1_find_tail, "find-tail", 2, 0, 0,
   SCM_ASSERT (pred_tramp, pred, SCM_ARG1, FUNC_NAME);
 
   for ( ; scm_is_pair (lst); lst = SCM_CDR (lst))
-    if (scm_is_true (pred_tramp (pred, SCM_CAR (lst))))
+    if (scm_is_true_and_not_lisp_nil (pred_tramp (pred, SCM_CAR (lst))))
       return lst;
   SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (lst), lst, SCM_ARG2, FUNC_NAME, "list");
 
@@ -1121,7 +1125,7 @@ SCM_DEFINE (scm_srfi1_list_index, "list-index", 2, 0, 1,
       SCM_ASSERT (pred_tramp, pred, SCM_ARG1, FUNC_NAME);
 
       for ( ; scm_is_pair (list1); n++, list1 = SCM_CDR (list1))
-        if (scm_is_true (pred_tramp (pred, SCM_CAR (list1))))
+        if (scm_is_true_and_not_lisp_nil (pred_tramp (pred, SCM_CAR (list1))))
           return SCM_I_MAKINUM (n);
 
       /* not found, check below that list1 is a proper list */
@@ -1146,8 +1150,9 @@ SCM_DEFINE (scm_srfi1_list_index, "list-index", 2, 0, 1,
               argnum = 3;
               break;
             }
-          if (scm_is_true (pred_tramp (pred,
-                                       SCM_CAR (list1), SCM_CAR (list2))))
+          if (scm_is_true_and_not_lisp_nil (pred_tramp (pred,
+							SCM_CAR (list1),
+							SCM_CAR (list2))))
             return SCM_I_MAKINUM (n);
 
           list1 = SCM_CDR (list1);
@@ -1183,7 +1188,7 @@ SCM_DEFINE (scm_srfi1_list_index, "list-index", 2, 0, 1,
               SCM_SIMPLE_VECTOR_SET (vec, i, SCM_CDR (lst));  /* rest of lst */
             }
 
-          if (scm_is_true (scm_apply (pred, args, SCM_EOL)))
+          if (scm_is_true_and_not_lisp_nil (scm_apply (pred, args, SCM_EOL)))
             return SCM_I_MAKINUM (n);
         }
     }
@@ -1286,7 +1291,8 @@ SCM_DEFINE (scm_srfi1_lset_adjoin, "lset-adjoin", 2, 0, 1,
       elem = SCM_CAR (rest);
 
       for (l = lst; scm_is_pair (l); l = SCM_CDR (l))
-        if (scm_is_true (equal_tramp (equal, SCM_CAR (l), elem)))
+        if (scm_is_true_and_not_lisp_nil (equal_tramp (equal, SCM_CAR (l),
+						       elem)))
           goto next_elem; /* elem already in lst, don't add */
 
       SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P(l), lst, SCM_ARG2, FUNC_NAME, "list");
@@ -1343,7 +1349,8 @@ SCM_DEFINE (scm_srfi1_lset_difference_x, "lset-difference!", 2, 0, 1,
            r = SCM_CDR (r), argnum++)
         {
           for (b = SCM_CAR (r); scm_is_pair (b); b = SCM_CDR (b))
-            if (scm_is_true (equal_tramp (equal, elem, SCM_CAR (b))))
+            if (scm_is_true_and_not_lisp_nil (equal_tramp (equal, elem,
+							   SCM_CAR (b))))
               goto next_elem; /* equal to elem, so drop that elem */
 
           SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (b), b, argnum, FUNC_NAME,"list");
@@ -1385,7 +1392,7 @@ check_map_args (SCM argv,
       long elt_len;
       elt = SCM_SIMPLE_VECTOR_REF (argv, i);
 
-      if (!(scm_is_null (elt) || scm_is_pair (elt)))
+      if (!(scm_is_null_or_lisp_nil (elt) || scm_is_pair (elt)))
 	goto check_map_error;
 	
       elt_len = srfi1_ilength (elt);
@@ -1430,7 +1437,8 @@ scm_srfi1_map (SCM proc, SCM arg1, SCM args)
   SCM *pres = &res;
 
   len = srfi1_ilength (arg1);
-  SCM_GASSERTn ((scm_is_null (arg1) || scm_is_pair (arg1)) && len >= -1,
+  SCM_GASSERTn ((scm_is_null_or_lisp_nil (arg1) ||
+		 scm_is_pair (arg1)) && len >= -1,
 		g_srfi1_map,
 		scm_cons2 (proc, arg1, args), SCM_ARG2, s_srfi1_map);
   SCM_VALIDATE_REST_ARGUMENT (args);
@@ -1456,7 +1464,7 @@ scm_srfi1_map (SCM proc, SCM arg1, SCM args)
 		    scm_cons2 (proc, arg1, args), SCM_ARG1, s_srfi1_map);
       if (len < 0 || (len2 >= 0 && len2 < len))
 	len = len2;
-      SCM_GASSERTn ((scm_is_null (arg2) || scm_is_pair (arg2))
+      SCM_GASSERTn ((scm_is_null_or_lisp_nil (arg2) || scm_is_pair (arg2))
 		    && len >= 0 && len2 >= -1,
 		    g_srfi1_map,
 		    scm_cons2 (proc, arg1, args),
@@ -1501,7 +1509,8 @@ scm_srfi1_for_each (SCM proc, SCM arg1, SCM args)
 {
   long i, len;
   len = srfi1_ilength (arg1);
-  SCM_GASSERTn ((scm_is_null (arg1) || scm_is_pair (arg1)) && len >= -1,
+  SCM_GASSERTn ((scm_is_null_or_lisp_nil (arg1) ||
+		 scm_is_pair (arg1)) && len >= -1,
 		g_srfi1_for_each, scm_cons2 (proc, arg1, args),
 		SCM_ARG2, s_srfi1_for_each);
   SCM_VALIDATE_REST_ARGUMENT (args);
@@ -1528,7 +1537,7 @@ scm_srfi1_for_each (SCM proc, SCM arg1, SCM args)
 		    scm_cons2 (proc, arg1, args), SCM_ARG1, s_srfi1_for_each);
       if (len < 0 || (len2 >= 0 && len2 < len))
 	len = len2;
-      SCM_GASSERTn ((scm_is_null (arg2) || scm_is_pair (arg2))
+      SCM_GASSERTn ((scm_is_null_or_lisp_nil (arg2) || scm_is_pair (arg2))
 		    && len >= 0 && len2 >= -1,
 		    g_srfi1_for_each,
 		    scm_cons2 (proc, arg1, args),
@@ -1593,7 +1602,7 @@ SCM_DEFINE (scm_srfi1_member, "member", 2, 1, 0,
     }
   for (; !SCM_NULL_OR_NIL_P (lst); lst = SCM_CDR (lst))
     {
-      if (scm_is_true (equal_p (pred, x, SCM_CAR (lst))))
+      if (scm_is_true_and_not_lisp_nil (equal_p (pred, x, SCM_CAR (lst))))
 	return lst;
     }
   return SCM_BOOL_F;
@@ -1621,7 +1630,7 @@ SCM_DEFINE (scm_srfi1_assoc, "assoc", 2, 1, 0,
       SCM tmp = SCM_CAR (ls);
       SCM_ASSERT_TYPE (scm_is_pair (tmp), alist, SCM_ARG2, FUNC_NAME,
 		       "association list");
-      if (scm_is_true (equal_p (pred, key, SCM_CAR (tmp))))
+      if (scm_is_true_and_not_lisp_nil (equal_p (pred, key, SCM_CAR (tmp))))
 	return tmp;
     }
   SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (ls), alist, SCM_ARG2, FUNC_NAME,
@@ -1685,7 +1694,7 @@ SCM_DEFINE (scm_srfi1_partition, "partition", 2, 0, 0,
     elt = SCM_CAR (list);
     new_tail = scm_cons (SCM_CAR (list), SCM_EOL);
 
-    if (scm_is_true (call (pred, elt))) {
+    if (scm_is_true_and_not_lisp_nil (call (pred, elt))) {
       SCM_SETCDR(kept_tail, new_tail);
       kept_tail = new_tail;
     }
@@ -1737,7 +1746,7 @@ SCM_DEFINE (scm_srfi1_partition_x, "partition!", 2, 0, 0,
 
   for ( ; scm_is_pair (lst); lst = SCM_CDR (lst))
     {
-      if (scm_is_true (pred_tramp (pred, SCM_CAR (lst))))
+      if (scm_is_true_and_not_lisp_nil (pred_tramp (pred, SCM_CAR (lst))))
         {
           *tp = lst;
           tp = SCM_CDRLOC (lst);
@@ -1906,7 +1915,7 @@ SCM_DEFINE (scm_srfi1_remove, "remove", 2, 0, 0,
        scm_is_pair (walk);
        walk = SCM_CDR (walk))
     {
-      if (scm_is_false (call (pred, SCM_CAR (walk))))
+      if (scm_is_false_or_lisp_nil (call (pred, SCM_CAR (walk))))
 	{
 	  *prev = scm_cons (SCM_CAR (walk), SCM_EOL);
 	  prev = SCM_CDRLOC (*prev);
@@ -1938,7 +1947,7 @@ SCM_DEFINE (scm_srfi1_remove_x, "remove!", 2, 0, 0,
        scm_is_pair (walk);
        walk = SCM_CDR (walk))
     {
-      if (scm_is_false (call (pred, SCM_CAR (walk))))
+      if (scm_is_false_or_lisp_nil (call (pred, SCM_CAR (walk))))
 	prev = SCM_CDRLOC (walk);
       else
 	*prev = SCM_CDR (walk);
@@ -1987,7 +1996,7 @@ SCM_DEFINE (scm_srfi1_span, "span", 2, 0, 0,
   for ( ; scm_is_pair (lst); lst = SCM_CDR (lst))
     {
       SCM elem = SCM_CAR (lst);
-      if (scm_is_false (pred_tramp (pred, elem)))
+      if (scm_is_false_or_lisp_nil (pred_tramp (pred, elem)))
         goto done;
 
       /* want this elem, tack it onto the end of ret */
@@ -2019,7 +2028,7 @@ SCM_DEFINE (scm_srfi1_span_x, "span!", 2, 0, 0,
   p = &lst;
   for (upto = lst; scm_is_pair (upto); upto = SCM_CDR (upto))
     {
-      if (scm_is_false (pred_tramp (pred, SCM_CAR (upto))))
+      if (scm_is_false_or_lisp_nil (pred_tramp (pred, SCM_CAR (upto))))
         goto done;
 
       /* want this element */
@@ -2147,7 +2156,7 @@ SCM_DEFINE (scm_srfi1_take_while, "take-while", 2, 0, 0,
   for ( ; scm_is_pair (lst); lst = SCM_CDR (lst))
     {
       SCM elem = SCM_CAR (lst);
-      if (scm_is_false (pred_tramp (pred, elem)))
+      if (scm_is_false_or_lisp_nil (pred_tramp (pred, elem)))
         goto done;
 
       /* want this elem, tack it onto the end of ret */
@@ -2178,7 +2187,7 @@ SCM_DEFINE (scm_srfi1_take_while_x, "take-while!", 2, 0, 0,
   p = &lst;
   for (upto = lst; scm_is_pair (upto); upto = SCM_CDR (upto))
     {
-      if (scm_is_false (pred_tramp (pred, SCM_CAR (upto))))
+      if (scm_is_false_or_lisp_nil (pred_tramp (pred, SCM_CAR (upto))))
         goto done;
 
       /* want this element */