diff --git a/doc/libraries.org b/doc/libraries.org
index 8e1367d..8823e17 100644
--- a/doc/libraries.org
+++ b/doc/libraries.org
@@ -1,5 +1,7 @@
 #+title: on libraries
 
+* libraries and the file system
+
 R⁷RS leaves it unspecified how exactly libraries correspond to files:
 
 #+begin_quote
@@ -7,3 +9,11 @@ Programs and libraries are typically stored in files, although in some implement
 #+end_quote
 
 thus the implementation of ~define-library~ is open to much interpretation. we could possibly define libraries as first-class objects, or deal with them statically. the former case is appealing to me, as it could massively simplify interactive use.
+
+* semantics of declaration order
+
+mercifully, R⁷RS is similarly ambiguous when it comes to the significance of declaration order. the authors note explicitly example two equally acceptable approaches:
+
+#+begin_quote
+One possible implementation of libraries is as follows: _After all cond-expand library declarations are expanded, a new environment is constructed for the library consisting of all imported bindings._ The expressions from all begin, include and include-ci library declarations are expanded in that environment in the order in which they occur in the library. _Alternatively, cond-expand and import declarations may be processed in left to right order interspersed with the processing of other declarations_, with the environment growing as imported bindings are added to it by each import declaration.
+#+end_quote
diff --git a/gyehoek.cabal b/gyehoek.cabal
index b75cfcc..b4c6693 100644
--- a/gyehoek.cabal
+++ b/gyehoek.cabal
@@ -66,6 +66,7 @@ library
     Gyehoek.GenSym
     Gyehoek.Jalmot
     Gyehoek.Language
+    Gyehoek.Language.Common
     Gyehoek.Lift1
     Gyehoek.Options
     Gyehoek.Prelude
@@ -111,17 +112,17 @@ library
     , process
     , recursion-schemes
     , scientific
+    , semialign
     , string-interpolate
     , tardis
     , template-haskell
     , text
     , text-short
+    , these
     , typed-process
     , unordered-containers
     , vector
     , witherable
-    , semialign
-    , these
 
   hs-source-dirs:   src
   default-language: GHC2024
diff --git a/src/Gyehoek/Language/Common.hs b/src/Gyehoek/Language/Common.hs
new file mode 100644
index 0000000..14d7c57
--- /dev/null
+++ b/src/Gyehoek/Language/Common.hs
@@ -0,0 +1,64 @@
+{-# LANGUAGE DeriveAnyClass #-}
+module Gyehoek.Language.Common
+  (
+  -- * Syntax
+    Lib(..)
+  , LibName(..)
+  , Exports
+  , Imports
+  , ExternName(..)
+  , Name(..)
+  ) where
+
+import Gyehoek.Prelude
+import Data.String (IsString)
+import Gyehoek.GenSym (Gen)
+import qualified Gyehoek.Sexp as S
+
+
+-- | R⁷RS 라이프러리의 표현.
+data Lib name body = MkLib
+  { name :: LibName
+  , exports :: Exports name
+  , imports :: Imports name
+  }
+  deriving (Show)
+
+newtype LibName = MkLibName { getLibName :: NonEmpty Text }
+  deriving stock (Show, Generic, Data, Eq)
+  deriving anyclass (NFData, Hashable)
+
+-- | A map whose keys are names of library definitions and whose
+-- values are the names they are exported as. An @⟨identifier⟩@ @x@
+-- corresponds to an entry @(⟨identifier⟩, ⟨identifier⟩)@, while a
+-- @(rename ⟨identifier₁⟩ ⟨identifier₂⟩)@ form corresponds to an entry
+-- @(⟨identifier₁⟩, ⟨identifier₂⟩)@.
+type Exports name = HashMap name ExternName
+
+-- | A map whose keys are symbols to be brought into the library's
+-- environment and whose values are pairs of the library in which the
+-- symbol is defined and the name the symbol is exported as.
+type Imports name = HashMap name (LibName, ExternName)
+
+-- | Representation of an identifier at the library boundary. While
+-- 'Name's are used within a compilation unit and may be decorated
+-- with additional structure and metadata, they are exported as
+-- 'ExternName's, which are essentially just plain strings.
+newtype ExternName = MkExternName { getExternName :: Text }
+  deriving newtype (Show)
+
+newtype Name = MkName { inner :: Text }
+  deriving newtype (Show, Eq, Ord, IsString, Gen, Hashable)
+  deriving stock (Generic, Data)
+  deriving anyclass (Wrapped, NFData)
+
+instance Prefixed Name where
+  prefixed (MkName s) = _Wrapped' . prefixed @Text s . from _Wrapped'
+
+
+--- DatumIsos
+
+instance S.DatumIso Name where
+  datumIso = S.decorate S.SynVariable
+    >>> S.symbol
+    >>> S.iso coerce coerce