diff --git a/Presentation/Yeamer.hs b/Presentation/Yeamer.hs
--- a/Presentation/Yeamer.hs
+++ b/Presentation/Yeamer.hs
@@ -47,14 +47,19 @@
                            -- ** Haskell values
                            , InteractiveShow(..)
                            -- ** Interactive parameters
-                           , inputBox, feedback_
+                           , inputBox, dropdownSelect, feedback_
                            -- * Structure / composition
                            , addHeading, (======), discardResult
                            , module Data.Monoid
                            , module Data.Semigroup.Numbered
-                           , (→│←)
                            , (→│)
+                           , (↘──)
+                           , (│←)
+                           , (──↖)
+                           , (→│←)
+                           , (↘──↖)
                            , (→│→)
+                           , (↘──↘)
                            -- * CSS
                            , divClass, divClasses, spanClass, (#%), styling, Css
                            -- * Server configuration
@@ -62,6 +67,8 @@
                            , YeamerServerConfig
                            -- | Default port is 14910
                            , yeamerTcpPort
+                           -- * Internals
+                           , IPresentation
                            ) where
 
 import Yesod hiding (get)
@@ -88,7 +95,7 @@
 import Presentation.Yeamer.Internal.Grid
 
 import Text.Cassius (cassius, Css)
-import Text.Julius (rawJS, Javascript)
+import Text.Julius (rawJS, Javascript, renderJavascript)
 
 import Yesod.Static (Static, static, base64md5)
 import Yesod.EmbeddedStatic
@@ -135,7 +142,8 @@
 
 import System.FilePath ( takeFileName, takeExtension, takeBaseName, dropExtension
                        , (<.>), (</>) )
-import System.Directory ( doesPathExist, makeAbsolute
+import System.IO.Error (catchIOError, isAlreadyExistsError)
+import System.Directory ( doesPathExist, canonicalizePath, removeFile
                         , createDirectoryIfMissing, renameFile
 #if MIN_VERSION_directory(1,3,1)
                         , createFileLink, pathIsSymbolicLink, getSymbolicLinkTarget
@@ -184,10 +192,11 @@
 
 data IPresentation m r where
    StaticContent :: Html -> IPresentation m ()
+   DynamicContent :: m Html -> IPresentation m ()
    TweakableInput :: (Sessionable x, JSON.FromJSON x)
         => Maybe x
-         -> ( PrPath -> ( Text   -- ^ The “final leaf” of the DOM path
-                      , Maybe x -> -- ^ An already stored value
+         -> ( PrPath -> ( Text   -- The “final leaf” of the DOM path
+                      , Maybe x -> -- An already stored value
                          ( PresProgress -> JavascriptUrl (Route PresentationServer)
                          , Html )
                       ))
@@ -237,6 +246,7 @@
 
 preprocPres :: IPresentation m r -> IPresentation m r
 preprocPres (StaticContent c) = StaticContent c
+preprocPres (DynamicContent c) = DynamicContent c
 preprocPres (TweakableInput defV frm) = TweakableInput defV frm
 preprocPres (Resultless p) = Resultless $ preprocPres p
 preprocPres (Styling s p) = Styling s $ preprocPres p
@@ -248,7 +258,7 @@
            = Styling grids
            . fmap ff
            . divClass gridClass
-           . Encaps ManualCSSClasses (backonstruct . map (first (read . Txt.unpack . _hchunkCSSClass) . swap)
+           . Encaps ManualCSSClasses (fst . backonstruct . map (first (read . Txt.unpack . _hchunkCSSClass) . swap)
                       . runWriterT)
            $ preprocPres <$> layouted
  where (GridLayout w h prelayed, backonstruct) = layoutGridP p
@@ -292,6 +302,7 @@
 
 isInline :: IPresentation m a -> Bool
 isInline (StaticContent _) = True
+isInline (DynamicContent _) = True
 isInline (TweakableInput _ _) = False
 isInline (Encaps ManualCSSClasses _ (WriterT qs)) = all (\(_,i) -> case i of
                    HTMSpan _ -> True
@@ -318,7 +329,7 @@
       slideChoice <- (`runReaderT`pPosition)
             $ chooseSlide "" defaultChoiceName "" Nothing Nothing presentation
       (`here`slideChoice) $ \slide -> do
-          let contents = go 0 slide
+          contents <- liftIO $ go 0 slide
           toWidget contents
       return ()
  where chooseSlide :: PrPath -> (Text->PrPath) -> Text -> Maybe PrPath -> Maybe PrPath
@@ -327,6 +338,8 @@
                             (WidgetT PresentationServer IO) (These Presentation r)
        chooseSlide _ _ "" Nothing Nothing (StaticContent conts)
            = pure $ These (StaticContent conts) ()
+       chooseSlide _ _ "" Nothing Nothing (DynamicContent conts)
+           = pure $ These (DynamicContent conts) ()
        chooseSlide path choiceName pdiv Nothing Nothing (TweakableInput defV frm) = do
            let (leafNm, interactor) = frm path
                fullPath = path<>leafNm
@@ -379,7 +392,7 @@
           positionCh <- lookupProgress progPath
           case positionCh of
             Nothing -> do
-              liftIO . putStrLn $ "Not enter '"++Txt.unpack progPath++"'"
+              -- liftIO . putStrLn $ "Not enter '"++Txt.unpack progPath++"'"
               purity <- chooseSlide path choiceName (pdiv<>"0") bwd (Just progPath) def
               case preferThis purity of
                  Left pres -> pure . This $ discardResult pres
@@ -440,8 +453,9 @@
        chooseSlide _ _ _ _ _ (Pure x) = pure $ That x
        chooseSlide _ _ _ _ _ pres
           = error $ "Cannot display "++outerConstructorName pres
-       go :: Int -> IPresentation m r -> Html
-       go _ (StaticContent conts) = conts
+       go :: Monad m => Int -> IPresentation m r -> m Html
+       go _ (StaticContent conts) = pure conts
+       go _ (DynamicContent conts) = conts
        go _ (Pure _) = error $ "Error: impossible to render a slide of an empty presentation."
        go _ (Dependent _ _) = error $ "Internal error: un-selected Dependent option while rendering to HTML."
        go lvl (Deterministic _ conts) = go lvl conts
@@ -467,7 +481,8 @@
                | Just _ <- Txt.stripPrefix "autogrid_" c
                             = "autogrid "<>c
                | otherwise  = c
-       go lvl (Encaps (CustomEncapsulation (EncapsulableWitness _) f) _ conts) = f $ go lvl <$> conts
+       go lvl (Encaps (CustomEncapsulation (EncapsulableWitness _) f) _ conts)
+             = fmap f . forM conts $ go lvl
        go _ p = error $ outerConstructorName p <> " cannot be rendered."
 
 
@@ -480,8 +495,11 @@
 hchunkFor t p | isInline p  = HTMSpan t
               | otherwise   = HTMDiv t
 
-instance (Monoid r, Sessionable r) => SG.Semigroup (IPresentation m r) where
+instance (Monad m, Monoid r, Sessionable r) => SG.Semigroup (IPresentation m r) where
   StaticContent c <> StaticContent d = StaticContent $ c<>d
+  DynamicContent c <> DynamicContent d = DynamicContent $ liftA2 (<>) c d
+  StaticContent c <> DynamicContent d = DynamicContent $ (c<>)<$>d
+  DynamicContent c <> StaticContent d = DynamicContent $ (<>d)<$>c
   Encaps ManualCSSClasses ff₀ (WriterT elems₀) <> Encaps ManualCSSClasses ff₁ (WriterT elems₁)
      = Encaps ManualCSSClasses ff' . WriterT . disambiguate
            $ map (first $ fmap Left) elems₀ ++ map (first $ fmap Right) elems₁
@@ -507,7 +525,7 @@
       = Resultless (Encaps ManualCSSClasses id $ WriterT [(c,hchunkFor""c)]) <> Resultless p
   p <> q = Encaps ManualCSSClasses fold $ WriterT
              [(p, hchunkFor"anonymousCell-0"p), (q, hchunkFor"anonymousCell-1"q)]
-instance ∀ m . Monoid (IPresentation m ()) where
+instance ∀ m . Monad m => Monoid (IPresentation m ()) where
   mappend = (SG.<>)
   mempty = Resultless $ Encaps ManualCSSClasses id
                 (WriterT [] :: WriterT HTMChunkK [] (IPresentation m ()))
@@ -519,13 +537,41 @@
        . Encaps GriddedBlocks id
        $ GridDivisions [GridRegion<$>[ Just<$>l, const Nothing<$>r ]]
 
+infix 5 ↘──
+(↘──) :: (Sessionable a)
+    => IPresentation m a -> IPresentation m b -> IPresentation m a
+l↘──r = fmap (\(GridDivisions [[GridRegion (Just a)], [GridRegion Nothing]]) -> a)
+       . Encaps GriddedBlocks id
+       $ GridDivisions [[GridRegion $ Just<$>l], [GridRegion $ const Nothing<$>r]]
+
+infix 6 │←
+(│←) :: (Sessionable b)
+    => IPresentation m a -> IPresentation m b -> IPresentation m b
+l│←r = fmap (\(GridDivisions [[GridRegion Nothing, GridRegion (Just b)]]) -> b)
+       . Encaps GriddedBlocks id
+       $ GridDivisions [GridRegion<$>[ const Nothing<$>l, Just<$>r ]]
+
+infix 5 ──↖
+(──↖) :: (Sessionable b)
+    => IPresentation m a -> IPresentation m b -> IPresentation m b
+l──↖r = fmap (\(GridDivisions [[GridRegion Nothing, GridRegion (Just b)]]) -> b)
+       . Encaps GriddedBlocks id
+       $ GridDivisions [[GridRegion $ const Nothing<$>l], [GridRegion $ Just<$>r]]
+
 infix 6 →│→
-(→│→) :: (Sessionable a)
+(→│→) :: (Sessionable a, Monad m)
     => IPresentation m a -> (a -> IPresentation m ()) -> IPresentation m a
 l→│→r = Feedback $ \aFbq -> l →│ case aFbq of
                                   Just a -> r a
-                                  othing -> mempty
+                                  Nothing -> mempty
 
+infix 5 ↘──↘
+(↘──↘) :: (Sessionable a, Monad m)
+    => IPresentation m a -> (a -> IPresentation m ()) -> IPresentation m a
+l↘──↘r = Feedback $ \aFbq -> l ↘── case aFbq of
+                                  Just a -> r a
+                                  Nothing -> mempty
+
 infix 6 →│←
 (→│←) :: (Sessionable a, Sessionable b)
     => IPresentation m a -> IPresentation m b -> IPresentation m (a,b)
@@ -534,6 +580,14 @@
        . Encaps GriddedBlocks id
        $ GridDivisions [GridRegion<$>[Left<$>l, Right<$>r]]
 
+infix 5 ↘──↖
+(↘──↖) :: (Sessionable a, Sessionable b)
+    => IPresentation m a -> IPresentation m b -> IPresentation m (a,b)
+l↘──↖r = fmap (\(GridDivisions [[GridRegion (Left a)], [GridRegion (Right b)]])
+                 -> (a,b))
+       . Encaps GriddedBlocks id
+       $ GridDivisions [[GridRegion $ Left<$>l], [GridRegion $ Right<$>r]]
+
 instance ∀ m . SemigroupNo 0 (IPresentation m ()) where
   sappendN _ (Resultless (Encaps GriddedBlocks _ l))
              (Resultless (Encaps GriddedBlocks _ r))
@@ -555,6 +609,7 @@
 
 outerConstructorName :: IPresentation m r -> String
 outerConstructorName (StaticContent _) = "StaticContent"
+outerConstructorName (DynamicContent _) = "DynamicContent"
 outerConstructorName (TweakableInput _ _) = "TweakableInput"
 outerConstructorName (Resultless _) = "Resultless"
 outerConstructorName (Styling _ _) = "Styling"
@@ -569,12 +624,16 @@
 
 discardResult :: IPresentation m r -> IPresentation m ()
 discardResult (StaticContent c) = StaticContent c
+discardResult (DynamicContent c) = DynamicContent c
 discardResult (Resultless p) = Resultless p
 discardResult p = Resultless p
 
 feedback_ :: Sessionable a => (Maybe a -> IPresentation m a) -> IPresentation m ()
 feedback_ = discardResult . Feedback
 
+-- | Run a monadic action and use the result in the presentation.
+--   Note that the action may not be re-run even if it depends to other
+--   values chosen at another point in the presentation, so use with care.
 serverSide :: Sessionable a => m a -> IPresentation m a
 serverSide = Interactive (pure ())
 
@@ -591,11 +650,13 @@
 instance ∀ m . Monad (IPresentation m) where
   return = pure
   StaticContent c >>= f = Dependent (StaticContent c) f
+  DynamicContent c >>= f = Dependent (DynamicContent c) f
   TweakableInput defV frm >>= f = Dependent (TweakableInput defV frm) f
   Resultless p >>= f = Dependent (Resultless p) f
   Feedback p >>= f = Dependent (Feedback p) f
   Styling _ (Pure x) >>= f = f x
   Styling s (StaticContent c) >>= f = Dependent (Styling s (StaticContent c)) f
+  Styling s (DynamicContent c) >>= f = Dependent (Styling s (DynamicContent c)) f
   Styling s (Resultless c) >>= f = Dependent (Styling s (Resultless c)) f
   Styling s (Styling s' x) >>= f = Styling (s++s') x >>= f
   Styling s (Encaps (WithHeading h) ff x) >>= f
@@ -669,10 +730,16 @@
                               $ f . runIdentity) runIdentity
                . Identity
 
+type JSCode url0 = (url0 -> [(Text,Text)] -> Text) -> Javascript
+
 class Sessionable i => Inputtable i where
   inputElemHtml :: i      -- ^ Current value
                 -> String -- ^ id in the DOM
                 -> Html
+  inputElemJSRead :: String   -- ^ id in the DOM
+                  -> Javascript -- ^ Expression that reads out the value
+  inputElemJSRead inputElId
+      = [julius| $("#{rawJS inputElId}").val() |](\_ _ -> mempty)
 
 instance Inputtable Int where
   inputElemHtml currentVal hashedId = [hamlet|
@@ -684,7 +751,14 @@
         <input type="number" id="#{hashedId}" value=#{currentVal} step="any">
        |]()
 
-inputBox :: (Inputtable i, JSON.FromJSON i) => i -> IPresentation m i
+instance Inputtable String where
+  inputElemHtml currentVal hashedId = [hamlet|
+        <input type="string" id="#{hashedId}" value=#{currentVal}>
+       |]()
+  inputElemJSRead inputElId
+      = [julius| JSON.stringify($("#{rawJS inputElId}").val()) |](\_ _ -> mempty)
+
+inputBox :: ∀ i m . (Inputtable i, JSON.FromJSON i) => i -> IPresentation m i
 inputBox iDef = fmap (maybe iDef id) . TweakableInput (Just iDef) $ \path ->
       let hashedId = base64md5 . BSL.fromStrict $ Txt.encodeUtf8 path
           inputElId = "input#"++hashedId
@@ -693,12 +767,13 @@
             let currentVal = case prevInp of
                  Nothing -> iDef
                  Just v -> v
+                valueReader = rawJS . renderJavascript $ inputElemJSRead @i inputElId
             in ( \pPosition -> [julius|
                  $("#{rawJS inputElId}").click(function(e){
                      e.stopPropagation();
                    })
                  $("#{rawJS inputElId}").change(function(e){
-                     currentVal = $("#{rawJS inputElId}").val()
+                     currentVal = #{valueReader}
                      pChanger =
                           "@{SetValR pPosition path NoValGiven}".slice(0, -1)
                                 // The slice hack removes the `NoValGiven`, to
@@ -731,12 +806,91 @@
                ) )
  where leafNm = " input"
 
+dropdownSelect :: ∀ a m . (a -> String) -> [a] -> Int -> IPresentation m a
+dropdownSelect valShow options iDef
+  | iDef>=0 && iDef<length options
+      = fmap ((options!!) . maybe iDef id) . TweakableInput (Just iDef) $ \path ->
+       let hashedId = base64md5 . BSL.fromStrict $ Txt.encodeUtf8 path
+           selectElId = "select#"++hashedId
+       in ( leafNm
+          , \prevInp ->
+             let currentIndex = case prevInp of
+                  Nothing -> iDef
+                  Just i -> i
+             in ( \pPosition -> [julius|
+                  $("#{rawJS selectElId}").click(function(e){
+                      e.stopPropagation();
+                    })
+                  $("#{rawJS selectElId}").change(function(e){
+                      currentVal = $("#{rawJS selectElId}").val()
+                      pChanger =
+                           "@{SetValR pPosition path NoValGiven}".slice(0, -1)
+                                 // The slice hack removes the `NoValGiven`, to
+                                 // be replaced with the actual value:
+                           + currentVal;
+                      e.stopPropagation();
+                      hasErrored = false;
+                      $.ajax({
+                            contentType: "application/json",
+                            processData: false,
+                            url: pChanger,
+                            type: "GET",
+                            dataType: "text",
+                            success: function(newURL, textStatus, jqXHR) {
+                               window.location.href = newURL;
+                            },
+                            error: function(jqXHR, textStatus, errorThrown) {
+                               $("body").css("cursor","not-allowed");
+                               hasErrored = true;
+                               setTimeout(function() {
+                                  $("body").css("cursor","auto")}, 500);
+                            }
+                         });
+                      setTimeout(function() {
+                          if (!hasErrored) {$("body").css("cursor","wait")}
+                      }, 150);
+                  })
+                       |]
+                , let ixedOptions = zip [0..] $ valShow<$>options
+                      isCurrentIndex = (==currentIndex)
+                  in [hamlet|
+                      <select id="#{hashedId}">
+                        $forall (i, optionStr) <- ixedOptions
+                           $if isCurrentIndex i
+                              <option value="#{i}" selected>
+                                 #{optionStr}
+                           $else
+                              <option value="#{i}">
+                                 #{optionStr}
+                      |]()
+                ) )
+  | otherwise  = error "Default selection for dropdown not included in options list."
+ where leafNm = " select"
+
 infixr 6 $<>
-($<>) :: (r ~ (), TMM.SymbolClass σ, TMM.SCConstraint σ LaTeX)
+
+-- | Include a mathematical expression inline in the document.
+($<>) :: (r ~ (), TMM.SymbolClass σ, TMM.SCConstraint σ LaTeX, Monad m)
          => TMM.CAS (TMM.Infix LaTeX) (TMM.Encapsulation LaTeX) (TMM.SymbolD σ LaTeX)
            -> IPresentation m r -> IPresentation m r
 ($<>) = (<>) . renderTeXMaths MathML.DisplayInline . TMM.toMathLaTeX
 
+-- | Include a mathematical expression as a “display” in the document, typically used for equations.
+-- 
+--   Example:
+-- 
+--   @
+--     "The constant "<>π$<>" fulfills "
+--       <>maths [[ sin π⩵0 ]]"."
+--   @
+-- 
+--   The maths expressions use TeX-my-maths syntax ("Math.LaTeX.Prelude").
+--   Note that TeX-my-maths has different syntax flavours (e.g. @𝑎×𝑒◝γ@ vs. @a * exp gamma@).
+--   Both can be used with '$<>' and 'maths', but the downside is type ambiguity
+--   in expressions that include no symbols at all (e.g. single numbers), which can lead to
+--   @Could not deduce ‘SymbolClass σ’@ compiler errors. To avoid this problem, you
+--   can add local type signatures or use the "Presentation.Yeamer.Maths.Unicode.MathLatin_RomanGreek"
+--   module.
 maths :: (r ~ (), TMM.SymbolClass σ, TMM.SCConstraint σ LaTeX)
         => [[TMM.CAS (TMM.Infix LaTeX) (TMM.Encapsulation LaTeX) (TMM.SymbolD σ LaTeX)]]
           -> String -> IPresentation m r
@@ -795,9 +949,11 @@
        
 -- | Display an image generated on-the-fly in the server. The image will be
 --   stored temporarily, in a content-indexed fashion.
-imageFromFileSupplier :: String               -- ^ File extension
-                      -> (FilePath -> IO ())  -- ^ File-writer function
-                      -> IPresentation IO ()
+imageFromFileSupplier
+   :: String               -- ^ File extension
+   -> (FilePath -> IO ())  -- ^ File-writer function. This will be called every time
+                           --   a slide with the image is requested.
+   -> IPresentation IO ()
 imageFromFileSupplier ext = includeMediaFile SimpleImage ext . Left
 
 -- | Display an image that lies on the server as any ordinary static file.
@@ -841,14 +997,13 @@
 
 includeMediaFile :: FileUsageSetup -> FilePath
              -> Either (FilePath -> IO ()) FilePath -> IPresentation IO ()
-includeMediaFile mediaSetup fileExt fileSupp = do
+includeMediaFile mediaSetup fileExt fileSupp = DynamicContent $ do
    let prepareServing file hashLen completeHash = do
          let linkPath = pStatDir</>take hashLen completeHash<.>takeExtension file
          isOccupied <- doesPathExist linkPath
-         absOrig <- makeAbsolute file
          let codedName = takeBaseName linkPath
              makeThisLink = do
-               createFileLink absOrig linkPath
+               createFileLink file linkPath
                return codedName
              disambiguate
               | hashLen < length linkPath  = prepareServing file (hashLen+1) completeHash
@@ -858,26 +1013,33 @@
               if isSymlk
                 then do
                   existingTgt <- getSymbolicLinkTarget linkPath
-                  if existingTgt/=absOrig
-                   then disambiguate
+                  if existingTgt/=file
+                   then error $ "Hash collision for path `"<>linkPath<>"` between files `"<>existingTgt<>"` and `"<>file<>"`"
                    else return codedName
-                else disambiguate
-            else makeThisLink
+                else error $ "A non-link file in occupies the needed path `"<>linkPath<>"`"
+            else do
+              catchIOError makeThisLink $ \e -> do
+                 if isAlreadyExistsError e
+                  then do
+                   removeFile linkPath -- must have been a dead link anyway, else it
+                   makeThisLink        -- would have already triggered `doesPathExist`.
+                  else
+                   error $ "Unknown problem when creating link `"<>linkPath<>"`"
    imgCode <- case fileSupp of
-       Right file
-          -> serverSide . prepareServing file 4 . base64md5 . BSL.fromStrict . BC8.pack
-                 $ show file
-       Left supplier
-          -> serverSide $ do
+       Right file -> do
+         absOrig <- canonicalizePath file
+         prepareServing absOrig 10 . base64md5 . BSL.fromStrict . BC8.pack
+                 $ show absOrig
+       Left supplier -> do
                tmpFile <- emptyTempFile pStatDir fileExt
                supplier tmpFile
                longHash <- base64md5 <$> BSL.readFile tmpFile
                let file = pStatDir</>longHash<.>fileExt
                renameFile tmpFile file
-               prepareServing file 4 (base64md5 . BSL.fromStrict $ BC8.pack file)
+               prepareServing file 10 (base64md5 . BSL.fromStrict $ BC8.pack file)
                
    let servableFile = "/pseudostatic"</>imgCode<.>fileExt
-    in StaticContent $ case mediaSetup of
+   return $ case mediaSetup of
          SimpleImage -> [hamlet| <img src=#{servableFile}> |]()
          SimpleVideo -> [hamlet| <video src=#{servableFile} controls> |]()
          CustomFile use -> use servableFile
@@ -910,6 +1072,7 @@
                            ( Maybe r  -- Key value this branch yields
                            , Bool )   -- Whether it contains displayable content
        go _ [] (StaticContent _) = return $ (Just (), True)
+       go _ [] (DynamicContent _) = return $ (Just (), True)
        go (crumbh,choiceName,crumbp) [] (TweakableInput defV twInp) = do
           let (pathFin, _) = twInp crumbh
               fullPath = crumbh<>pathFin
@@ -1036,6 +1199,7 @@
        skipContentless crumbs (Deterministic f c)
            = fmap f <$> skipContentless crumbs c
        skipContentless _ (StaticContent _) = return Nothing
+       skipContentless _ (DynamicContent _) = return Nothing
        skipContentless _ (Encaps _ _ _) = return Nothing
        skipContentless _ p = error
         $ "`skipContentless` does not support "++outerConstructorName p
@@ -1058,6 +1222,7 @@
        hasDisplayableContent crumbs (Deterministic f c)
            = hasDisplayableContent crumbs c
        hasDisplayableContent _ (StaticContent _) = return True
+       hasDisplayableContent _ (DynamicContent _) = return True
        hasDisplayableContent _ (Encaps _ _ _) = return True
        hasDisplayableContent _ p = error
         $ "`hasDisplayableContent` does not support "++outerConstructorName p
diff --git a/Presentation/Yeamer/Internal/Grid.hs b/Presentation/Yeamer/Internal/Grid.hs
--- a/Presentation/Yeamer/Internal/Grid.hs
+++ b/Presentation/Yeamer/Internal/Grid.hs
@@ -86,34 +86,36 @@
 type GridRegionId = Int
 
 layoutGridP :: Gridded a -> ( GridLayout (GridRegionId, a)
-                            , [(GridRegionId, b)] -> Gridded b )
+                            , [(GridRegionId, b)] -> (Gridded b, [(GridRegionId, b)]) )
 layoutGridP = (`evalState`0) . go
  where go (GridRegion a) = do
          i <- get
          put $ i+1
          return ( GridLayout 1 1 [(GridRange 0 1 0 1, (i, a))]
-                , \[(_, b)] -> GridRegion b )
-       go (GridDivisions [[GridRegion a₀, GridRegion a₁]]) = do
-         i <- get
-         put $ i+2
-         return ( GridLayout 2 1 [ (GridRange 0 1 0 1, (i, a₀))
-                                 , (GridRange 1 2 0 1, (i+1, a₁)) ]
-                , \[(_,b₀), (_,b₁)] -> GridDivisions [[GridRegion b₀,GridRegion b₁]] )
+                , \((_, b):lgrs) -> (GridRegion b, lgrs) )
        go (GridDivisions []) 
         = return ( GridLayout 0 0 []
-                 , \[] -> GridDivisions [] )
+                 , \lgrs -> (GridDivisions [], lgrs) )
        go (GridDivisions [row]) = do
          layouts <- mapM go row
          return ( alignLayoutDirectional gridWidth xBegin xEnd
                              gridHeight yBegin yEnd
                              (fst<$>layouts)
-                , undefined )
+                , let procLgrs [] acc lgrs = (GridDivisions [acc []], lgrs)
+                      procLgrs (srow:srows) acc lgrs
+                         = let (srowRes, lgrs') = srow lgrs
+                           in procLgrs srows (acc . (srowRes:)) lgrs'
+                  in procLgrs (snd<$>layouts) id )
        go (GridDivisions rows) = do
          rLayouts <- mapM (go . GridDivisions . pure) rows
          return ( alignLayoutDirectional gridHeight yBegin yEnd
                              gridWidth xBegin xEnd
                         (fst<$>rLayouts)
-                , undefined )
+                , let procLgrs [] acc lgrs = (GridDivisions $ acc [], lgrs)
+                      procLgrs (srow:srows) acc lgrs
+                         = let (GridDivisions [srowRes], lgrs') = srow lgrs
+                           in procLgrs srows (acc . (srowRes:)) lgrs'
+                  in procLgrs (snd<$>rLayouts) id  )
 
 alignLayoutDirectional
     :: Lens' (GridLayout a) Int -> Lens' GridRange Int -> Lens' GridRange Int
diff --git a/Presentation/Yeamer/Maths/Unicode/MathLatin_RomanGreek.hs b/Presentation/Yeamer/Maths/Unicode/MathLatin_RomanGreek.hs
new file mode 100644
--- /dev/null
+++ b/Presentation/Yeamer/Maths/Unicode/MathLatin_RomanGreek.hs
@@ -0,0 +1,49 @@
+-- |
+-- Module      : Presentation.Yeamer.Maths.Unicode.MathLatin_RomanGreek
+-- Copyright   : (c) Justus Sagemüller 2017
+-- License     : GPL v3
+-- 
+-- Maintainer  : (@) jsag $ hvl.no
+-- Stability   : experimental
+-- Portability : portable
+-- 
+-- Convenience module, re-exporting the necessary LaTeX builders for writing maths
+-- in a Yeamer presentation.
+
+{-# LANGUAGE CPP            #-}
+{-# LANGUAGE TypeFamilies   #-}
+
+module Presentation.Yeamer.Maths.Unicode.MathLatin_RomanGreek
+                ( module Presentation.Yeamer
+                , module Math.LaTeX.Prelude
+                , module Math.LaTeX.StringLiterals
+                , Presentation.Yeamer.Maths.Unicode.MathLatin_RomanGreek.maths
+                , (Presentation.Yeamer.Maths.Unicode.MathLatin_RomanGreek.$<>)
+                , Math
+                ) where
+
+
+import Presentation.Yeamer hiding (($<>), maths)
+import qualified Presentation.Yeamer.Maths as YMth
+import Math.LaTeX.Prelude hiding ( maths
+#if MIN_VERSION_TeX_my_math(0,201,2)
+                                 , ($<>)
+#endif
+                                 )
+import CAS.Dumb (CAS, Encapsulation, Infix)
+import CAS.Dumb.Symbols.Unicode.MathLatin_RomanGreek__BopomofoGaps
+           as UnicodeMth
+import Math.LaTeX.StringLiterals ()
+import Text.LaTeX (LaTeX)
+
+type Math = Expression LaTeX
+
+($<>) :: CAS (Infix LaTeX) (Encapsulation LaTeX) (UnicodeMth.Symbol LaTeX)
+              -> Presentation -> Presentation
+($<>) = (YMth.$<>)
+
+maths :: r ~ ()
+        => [[CAS (Infix LaTeX) (Encapsulation LaTeX) (UnicodeMth.Symbol LaTeX)]]
+          -> String -> IPresentation m r
+maths = YMth.maths
+
diff --git a/test/Main.hs b/test/Main.hs
--- a/test/Main.hs
+++ b/test/Main.hs
@@ -85,6 +85,14 @@
                    -> fromString ("Sum is "<>show (i+j))
                  )
 
+   "Dropdown selectors"
+    ====== do
+    (const() <$> dropdownSelect @Int show [1,3,9] 0
+       →│→ \i -> fromString $ "Value is "<>show i)
+     ──
+     (const() <$> dropdownSelect @String id ["bla","bli","blub"] 2
+       →│→ \s -> fromString $ "You say “"<>s<>"”")
+
    "Code block"
     ====== [plaintext|
        bla
diff --git a/yeamer.cabal b/yeamer.cabal
--- a/yeamer.cabal
+++ b/yeamer.cabal
@@ -2,7 +2,7 @@
 -- documentation, see http://haskell.org/cabal/users-guide/
 
 name:                yeamer
-version:             0.1.1.0
+version:             0.1.2.0
 synopsis:            Yesod-based server for interactive presentation slides
 -- description:         
 homepage:            https://github.com/leftaroundabout/yeamer
@@ -19,13 +19,14 @@
 library
   exposed-modules:     Presentation.Yeamer
                        Presentation.Yeamer.Maths
+                       Presentation.Yeamer.Maths.Unicode.MathLatin_RomanGreek
                        Presentation.Yeamer.Internal.Grid
   other-modules:       Control.Monad.Trans.Writer.JSONable
                        Presentation.Yeamer.Internal.PrPathStepCompression
                        Presentation.Yeamer.Internal.Progress
                        Data.Traversable.Redundancy
   -- other-extensions:    
-  build-depends:       base >=4.8 && <4.14
+  build-depends:       base >=4.8 && <4.16
                        , yesod >=1.4 && <1.7
                        , yesod-form
                        , yesod-static