diff --git a/library/data_structures_[l,r)/bit.hpp b/library/data_structures_[l,r)/bit.hpp
index 4b6cc0be..0ee5f36c 100644
--- a/library/data_structures_[l,r)/bit.hpp
+++ b/library/data_structures_[l,r)/bit.hpp
@@ -1,4 +1,13 @@
 #pragma once
+//! @code
+//!   BIT bit(n);
+//!   bit.walk([&](int r, ll sum) -> bool {
+//!     // sum = a[0] + a[1] + ... + a[r - 1]
+//!   });
+//!   int r = bit.walk2(sum);
+//!   // Returns min r s.t. sum of [0,r] >= sum
+//!   // Returns n if sum of [0,n-1] < sum
+//! @endcode
 //! @time O(n + q log n)
 //! @space O(n)
 // NOLINTNEXTLINE(readability-identifier-naming)
diff --git a/library/data_structures_[l,r)/bit_uncommon/walk.hpp b/library/data_structures_[l,r)/bit_uncommon/walk.hpp
index 85d984d1..20c3a732 100644
--- a/library/data_structures_[l,r)/bit_uncommon/walk.hpp
+++ b/library/data_structures_[l,r)/bit_uncommon/walk.hpp
@@ -1,6 +1,3 @@
-//! Requires sum of [i,i] >= 0
-//! Returns min r s.t. sum of [0,r] >= sum
-//! Returns n if sum of [0,n-1] < sum
 int walk2(ll sum) {
   if (sum <= 0) return -1;
   int r = 0;
diff --git a/library/data_structures_[l,r]/bit.hpp b/library/data_structures_[l,r]/bit.hpp
index 72a77a7c..ba96de89 100644
--- a/library/data_structures_[l,r]/bit.hpp
+++ b/library/data_structures_[l,r]/bit.hpp
@@ -1,4 +1,13 @@
 #pragma once
+//! @code
+//!   BIT bit(n);
+//!   bit.walk([&](int r, ll sum) -> bool {
+//!     // sum = a[0] + a[1] + ... + a[r]
+//!   });
+//!   int r = bit.walk2(sum);
+//!   // Returns min r s.t. sum of [0,r] >= sum
+//!   // Returns n if sum of [0,n-1] < sum
+//! @endcode
 //! @time O(n + q log n)
 //! @space O(n)
 // NOLINTNEXTLINE(readability-identifier-naming)
@@ -17,5 +26,6 @@ struct BIT {
   ll query(int l, int r) {
     return query(r) - query(l - 1);
   }
+#include "bit_uncommon/walk_lambda.hpp"
 #include "../data_structures_[l,r)/bit_uncommon/walk.hpp"
 };
diff --git a/library/data_structures_[l,r]/bit_uncommon/walk_lambda.hpp b/library/data_structures_[l,r]/bit_uncommon/walk_lambda.hpp
new file mode 100644
index 00000000..a87ee4af
--- /dev/null
+++ b/library/data_structures_[l,r]/bit_uncommon/walk_lambda.hpp
@@ -0,0 +1,6 @@
+void walk(const auto& f) {
+  ll sum = 0;
+  for (int i = bit_floor(size(s)), r = 0; i; i /= 2)
+    if (r + i <= sz(s) && f(r + i - 1, sum + s[r + i - 1]))
+      sum += s[(r += i) - 1];
+}
diff --git a/tests/.config/.code_snippet_excluded_file_list b/tests/.config/.code_snippet_excluded_file_list
index f6dd52d1..6680d0b6 100644
--- a/tests/.config/.code_snippet_excluded_file_list
+++ b/tests/.config/.code_snippet_excluded_file_list
@@ -18,6 +18,7 @@ find_substrings_concatenated.hpp
 pascals_identity.hpp
 binary_search.hpp
 walk.hpp
+walk_lambda.hpp
 prev.hpp
 next.hpp
 wavelet_count_less.hpp
diff --git a/tests/.config/.cppcheck_suppression_list b/tests/.config/.cppcheck_suppression_list
index aa381399..79794aaa 100644
--- a/tests/.config/.cppcheck_suppression_list
+++ b/tests/.config/.cppcheck_suppression_list
@@ -61,5 +61,5 @@ unusedFunction:../kactl/content/data-structures/UnionFind.h:14
 unusedFunction:../kactl/content/number-theory/ModPow.h:13
 unusedFunction:../kactl/stress-tests/utilities/genTree.h:49
 containerOutOfBounds:../library/data_structures_[l,r)/uncommon/permutation_tree.hpp:85
-ctuOneDefinitionRuleViolation:../library/data_structures_[l,r)/bit.hpp:5
+ctuOneDefinitionRuleViolation:../library/data_structures_[l,r)/bit.hpp:14
 ctuOneDefinitionRuleViolation:../library/data_structures_[l,r)/lazy_seg_tree.hpp:4
diff --git a/tests/library_checker_aizu_tests/data_structures/bit.test.cpp b/tests/library_checker_aizu_tests/data_structures/bit.test.cpp
index f0353e12..3f80ba46 100644
--- a/tests/library_checker_aizu_tests/data_structures/bit.test.cpp
+++ b/tests/library_checker_aizu_tests/data_structures/bit.test.cpp
@@ -58,7 +58,7 @@ int main() {
       }
       return 1;
     };
-    assert(bit.walk(sum) == st.find_first(0, n, f));
+    assert(bit.walk2(sum) == st.find_first(0, n, f));
   }
   return 0;
 }
diff --git a/tests/library_checker_aizu_tests/data_structures/bit_inc_walk.test.cpp b/tests/library_checker_aizu_tests/data_structures/bit_inc_walk.test.cpp
new file mode 100644
index 00000000..f9d5cf87
--- /dev/null
+++ b/tests/library_checker_aizu_tests/data_structures/bit_inc_walk.test.cpp
@@ -0,0 +1,51 @@
+#define PROBLEM \
+  "https://judge.yosupo.jp/problem/predecessor_problem"
+#include "../template.hpp"
+#include "../../../library/data_structures_[l,r]/bit.hpp"
+int main() {
+  cin.tie(0)->sync_with_stdio(0);
+  int n, q;
+  string s;
+  cin >> n >> q >> s;
+  vector<ll> init(n);
+  for (int i = 0; i < n; i++) init[i] = s[i] - '0';
+  BIT bit(init);
+  while (q--) {
+    int type, k;
+    cin >> type >> k;
+    if (type == 0) {
+      if (bit.query(k, k) == 0) bit.update(k, 1);
+    } else if (type == 1) {
+      if (bit.query(k, k) == 1) bit.update(k, -1);
+    } else if (type == 2) {
+      cout << bit.query(k, k) << '\n';
+    } else if (type == 3) {
+      if (bit.query(k, n - 1) == 0) cout << -1 << '\n';
+      else {
+        ll order = bit.query(k - 1);
+        int res = -1;
+        bit.walk([&](int r, ll sum) {
+          if (sum <= order) return 1;
+          res = r;
+          return 0;
+        });
+        cout << res << '\n';
+      }
+    } else {
+      if (bit.query(k) == 0) cout << -1 << '\n';
+      else {
+        ll order = bit.query(k);
+        int res = -1;
+        bit.walk([&](int r, ll sum) {
+          if (sum >= order) {
+            res = r;
+            return 0;
+          }
+          return 1;
+        });
+        cout << res << '\n';
+      }
+    }
+  }
+  return 0;
+}
diff --git a/tests/library_checker_aizu_tests/data_structures/bit_ordered_set.test.cpp b/tests/library_checker_aizu_tests/data_structures/bit_ordered_set.test.cpp
index 3349d015..aeef3a5c 100644
--- a/tests/library_checker_aizu_tests/data_structures/bit_ordered_set.test.cpp
+++ b/tests/library_checker_aizu_tests/data_structures/bit_ordered_set.test.cpp
@@ -40,7 +40,7 @@ int main() {
       x = get_compressed_idx(x);
       if (bit.query(x, x) == 1) bit.update(x, -1);
     } else if (type == 2) {
-      int res = bit.walk(x);
+      int res = bit.walk2(x);
       if (res == -1 || res == ssize(compress))
         cout << -1 << '\n';
       else cout << compress[res] << '\n';
@@ -49,12 +49,12 @@ int main() {
       cout << bit.query(x) << '\n';
     } else if (type == 4) {
       x = get_compressed_idx(x);
-      int res = bit.walk(bit.query(x));
+      int res = bit.walk2(bit.query(x));
       if (res == -1) cout << -1 << '\n';
       else cout << compress[res] << '\n';
     } else {
       x = get_compressed_idx(x);
-      int res = bit.walk(bit.query(x - 1) + 1);
+      int res = bit.walk2(bit.query(x - 1) + 1);
       if (res == ssize(bit.s)) cout << -1 << '\n';
       else cout << compress[res] << '\n';
     }
diff --git a/tests/library_checker_aizu_tests/handmade_tests/seg_tree_find.test.cpp b/tests/library_checker_aizu_tests/handmade_tests/seg_tree_find.test.cpp
index 42248b64..9efea020 100644
--- a/tests/library_checker_aizu_tests/handmade_tests/seg_tree_find.test.cpp
+++ b/tests/library_checker_aizu_tests/handmade_tests/seg_tree_find.test.cpp
@@ -38,7 +38,7 @@ int main() {
       rngs.push_back({tl, tr, 1});
       return 1;
     };
-    int pos = min(bit.walk(bit.query(l) + sum), r);
+    int pos = min(bit.walk2(bit.query(l) + sum), r);
     reset();
     assert(pos == seg.find_first(l, r, f));
     assert(!empty(rngs));
diff --git a/tests/scripts/compile_commented_snippets.sh b/tests/scripts/compile_commented_snippets.sh
index 4d73abfc..785ace98 100755
--- a/tests/scripts/compile_commented_snippets.sh
+++ b/tests/scripts/compile_commented_snippets.sh
@@ -25,7 +25,7 @@ git submodule update
 	echo "vi rhs;"
 	echo "vector<vi> mat;"
 	echo "vector<vector<bool>> grid;"
-	echo "int n,m,k,tl,tr,l,r,l1,r1,l2,r2,s_l,s_r,root_l,root_r,source,sink,total_flow,bccid,u,v,w,lsz,rsz,cols,cap,num,x,y,i,j,i1,i2,j1,j2,len;"
+	echo "int n,m,k,tl,tr,l,r,l1,r1,l2,r2,s_l,s_r,root_l,root_r,source,sink,total_flow,bccid,u,v,w,lsz,rsz,cols,cap,num,x,y,i,j,i1,i2,j1,j2,len,sum;"
 } >entire_library_without_main
 
 {