diff --git a/Dvda.hs b/Dvda.hs
--- a/Dvda.hs
+++ b/Dvda.hs
@@ -13,6 +13,7 @@
 
 module Dvda ( -- * primitives
               sym
+            , symDependent
             , vsym
             , msym
             , svec
diff --git a/Dvda/Expr.hs b/Dvda/Expr.hs
--- a/Dvda/Expr.hs
+++ b/Dvda/Expr.hs
@@ -337,6 +337,9 @@
 sym :: String -> Expr DIM0 a
 sym = (ESym Z) . Sym
 
+-- | Symbolic scalar which is a function of some independent variable, like time.
+-- .
+-- This lets you do d(f(g(t)))/dt == f'(g(t))*g'(t)
 symDependent :: String -> Expr DIM0 a -> Expr DIM0 a
 symDependent name (ESym _ s)  = ESym Z (SymDependent name 0 s)
 symDependent _ _ = error "symDependent got non ESym dependency"
diff --git a/dvda.cabal b/dvda.cabal
--- a/dvda.cabal
+++ b/dvda.cabal
@@ -1,5 +1,5 @@
 Name:                dvda
-Version:             0.2.0
+Version:             0.2.1
 License:             BSD3
 License-file:        LICENSE
 Author:              Greg Horn