diff --git a/rainbowadn/inlining/ipair.py b/rainbowadn/inlining/ipair.py
index 04bf93b..8fce4be 100644
--- a/rainbowadn/inlining/ipair.py
+++ b/rainbowadn/inlining/ipair.py
@@ -28,3 +28,9 @@ class IPair(IAuto, Generic[E0, E1]):
         assert isinstance(v0, Mentionable)
         assert isinstance(v1, Mentionable)
         return cls.from_values(v0, v1)
+
+    @classmethod
+    def f(cls, f0: RainbowFactory[E0], f1: RainbowFactory[E1]) -> RainbowFactory['IPair[E0, E1]']:
+        assert isinstance(f0, RainbowFactory)
+        assert isinstance(f1, RainbowFactory)
+        return cls.factory(f0, f1)
diff --git a/rainbowadn/v13/signature.py b/rainbowadn/v13/signature.py
index acc9f56..127909f 100644
--- a/rainbowadn/v13/signature.py
+++ b/rainbowadn/v13/signature.py
@@ -2,8 +2,8 @@ import nacl.bindings
 import nacl.exceptions
 import nacl.signing
 
-from rainbowadn.atomic import *
 from rainbowadn.core import *
+from rainbowadn.inlining import *
 from .subject import *
 
 __all__ = ('BadSignature', 'Signature',)
@@ -13,12 +13,16 @@ class BadSignature(nacl.exceptions.BadSignatureError):
     pass
 
 
-class Signature(Atomic):
+class Signature(IAtomic):
     def __init__(self, source: bytes):
         assert isinstance(source, bytes)
         assert_eq(len(source), nacl.bindings.crypto_sign_BYTES)
         self.source = source
 
+    @classmethod
+    def size(cls) -> int:
+        return nacl.bindings.crypto_sign_BYTES
+
     @classmethod
     def empty(cls) -> 'Signature':
         return Signature(bytes(nacl.bindings.crypto_sign_BYTES))
diff --git a/rainbowadn/v13/subject.py b/rainbowadn/v13/subject.py
index 8e66535..42dd6a1 100644
--- a/rainbowadn/v13/subject.py
+++ b/rainbowadn/v13/subject.py
@@ -1,18 +1,23 @@
+import nacl.bindings
 from nacl.public import PublicKey
 from nacl.signing import VerifyKey
 
-from rainbowadn.atomic import *
+from rainbowadn.inlining import *
 
 __all__ = ('Subject',)
 
 
-class Subject(Atomic):
+class Subject(IAtomic):
     def __init__(self, verify_key: VerifyKey):
         assert isinstance(verify_key, VerifyKey)
         self.verify_key: VerifyKey = verify_key
         self.public_key: PublicKey = verify_key.to_curve25519_public_key()
         assert isinstance(self.public_key, PublicKey)
 
+    @classmethod
+    def size(cls) -> int:
+        return nacl.bindings.crypto_sign_PUBLICKEYBYTES
+
     @classmethod
     def _from_bytes(cls, source: bytes) -> 'Subject':
         assert isinstance(source, bytes)