diff --git a/include/bitcoin/system/chain/enums/magic_numbers.hpp b/include/bitcoin/system/chain/enums/magic_numbers.hpp
index de27b36b32..d15381dd47 100644
--- a/include/bitcoin/system/chain/enums/magic_numbers.hpp
+++ b/include/bitcoin/system/chain/enums/magic_numbers.hpp
@@ -36,7 +36,7 @@ constexpr uint64_t sighash_null_value = max_uint64;
 /// ---------------------------------------------------------------------------
 
 constexpr size_t max_counted_ops = 201;
-constexpr size_t max_stack_size = 1'000;
+constexpr size_t max_unified_stack_size = 1'000;
 constexpr size_t max_unified_script_size = 20'000;
 constexpr size_t max_script_size = to_half(max_unified_script_size);
 constexpr size_t max_push_data_size = 520;
diff --git a/include/bitcoin/system/chain/header.hpp b/include/bitcoin/system/chain/header.hpp
index 9dee4ec8fb..62eb9e8964 100644
--- a/include/bitcoin/system/chain/header.hpp
+++ b/include/bitcoin/system/chain/header.hpp
@@ -99,7 +99,7 @@ class BC_API header
 
     /// Computed properties.
     hash_digest hash() const NOEXCEPT;
-    uint256_t difficulty() const NOEXCEPT;
+    uint256_t proof() const NOEXCEPT;
 
     /// Cache (this overrides hash() computation).
     void set_hash(hash_digest&& hash) const NOEXCEPT;
@@ -136,7 +136,7 @@ class BC_API header
 
 private:
     static header from_data(reader& source) NOEXCEPT;
-    static uint256_t difficulty(uint32_t bits) NOEXCEPT;
+    static uint256_t proof(uint32_t bits) NOEXCEPT;
 
     // Header should be stored as shared (adds 16 bytes).
     // copy: 4 * 32 + 2 * 256 + 1 = 81 bytes (vs. 16 when shared).
diff --git a/include/bitcoin/system/impl/machine/program.ipp b/include/bitcoin/system/impl/machine/program.ipp
index 6407583e09..a2961ca64a 100644
--- a/include/bitcoin/system/impl/machine/program.ipp
+++ b/include/bitcoin/system/impl/machine/program.ipp
@@ -539,7 +539,7 @@ INLINE bool program<Stack>::
 is_stack_overflow() const NOEXCEPT
 {
     // Addition is safe due to stack size constraint.
-    return (stack_size() + alternate_.size()) > max_stack_size;
+    return (stack_size() + alternate_.size()) > max_unified_stack_size;
 }
 
 // private
diff --git a/src/chain/header.cpp b/src/chain/header.cpp
index fd16f59903..16188c01b5 100644
--- a/src/chain/header.cpp
+++ b/src/chain/header.cpp
@@ -252,7 +252,7 @@ hash_digest header::hash() const NOEXCEPT
 }
 
 // static/private
-uint256_t header::difficulty(uint32_t bits) NOEXCEPT
+uint256_t header::proof(uint32_t bits) NOEXCEPT
 {
     auto target = compact::expand(bits);
 
@@ -276,10 +276,10 @@ uint256_t header::difficulty(uint32_t bits) NOEXCEPT
 }
 
 // computed
-uint256_t header::difficulty() const NOEXCEPT
+uint256_t header::proof() const NOEXCEPT
 {
     // Returns zero if bits_ mantissa is less than one or bits_ is overflowed.
-    return difficulty(bits_);
+    return proof(bits_);
 }
 
 // Check.
@@ -307,7 +307,7 @@ bool header::is_invalid_proof_of_work(uint32_t proof_of_work_limit,
 }
 
 // ****************************************************************************
-/// CONSENSUS: bitcoin 32bit unix time: en.wikipedia.org/wiki/Year_2038_problem
+// CONSENSUS: bitcoin 32bit unix time: en.wikipedia.org/wiki/Year_2038_problem
 // ****************************************************************************
 bool header::is_invalid_timestamp(
     uint32_t timestamp_limit_seconds) const NOEXCEPT
diff --git a/test/chain/header.cpp b/test/chain/header.cpp
index 63221fd886..1cb5f0518d 100644
--- a/test/chain/header.cpp
+++ b/test/chain/header.cpp
@@ -240,10 +240,10 @@ BOOST_AUTO_TEST_CASE(header__to_data__writer__expected)
 
 // hash
 
-BOOST_AUTO_TEST_CASE(header__difficulty__genesis_block__expected)
+BOOST_AUTO_TEST_CASE(header__proof__genesis_block__expected)
 {
     const chain::block block{ settings(selection::mainnet).genesis_block };
-    BOOST_REQUIRE_EQUAL(block.header().difficulty(), 0x0000000100010001);
+    BOOST_REQUIRE_EQUAL(block.header().proof(), 0x0000000100010001);
 }
 
 // validation (public)