diff --git a/client/src/components/Inventory.tsx b/client/src/components/Inventory.tsx
index dd7f867..77768b7 100644
--- a/client/src/components/Inventory.tsx
+++ b/client/src/components/Inventory.tsx
@@ -73,17 +73,19 @@ function InventoryList({items, docType, openDoc, defaultTab=null, level=undefine
     ).map(item => {
         if ((tab ?? categories[0]) == item.category) {
           return <InventoryItem key={item.name} showDoc={() => {openDoc(item.name, docType)}}
-            name={item.name} displayName={item.displayName} locked={item.locked} disabled={item.disabled} />
+            name={item.name} displayName={item.displayName} locked={item.locked}
+            disabled={item.disabled} newly={item.new}/>
         }
       }) }
     </div>
     </>
 }
 
-function InventoryItem({name, displayName, locked, disabled, showDoc}) {
+function InventoryItem({name, displayName, locked, disabled, newly, showDoc}) {
   const icon = locked ? <FontAwesomeIcon icon={faLock} /> :
                disabled ? <FontAwesomeIcon icon={faBan} /> : ""
-  const className = locked ? "locked" : disabled ? "disabled" : ""
+  const className = newly ? "new" : "old"
+  // const className = locked ? "locked" : disabled ? "disabled" : newly ? "new" : ""
   const title = locked ? "Not unlocked yet" :
                 disabled ? "Not available in this level" : ""
 
diff --git a/client/src/components/inventory.css b/client/src/components/inventory.css
index 65eac26..2c5af05 100644
--- a/client/src/components/inventory.css
+++ b/client/src/components/inventory.css
@@ -26,6 +26,9 @@
   color: #ccc;
 }
 
+.inventory .item.new {
+  color: rgb(247, 216, 93);
+}
 
 .inventory .item:not(.locked):not(.disabled) {
   cursor: pointer;
diff --git a/client/src/state/api.ts b/client/src/state/api.ts
index 0cbc4be..3569fcb 100644
--- a/client/src/state/api.ts
+++ b/client/src/state/api.ts
@@ -15,7 +15,8 @@ export interface ComputedInventoryItem {
   displayName: string,
   category: string,
   disabled: boolean,
-  locked: boolean
+  locked: boolean,
+  new: boolean
 }
 
 export interface LevelInfo {
diff --git a/server/GameServer/Commands.lean b/server/GameServer/Commands.lean
index 692139b..5b94ff9 100644
--- a/server/GameServer/Commands.lean
+++ b/server/GameServer/Commands.lean
@@ -72,7 +72,7 @@ elab "Path" s:Parser.path : command => do
 
 /-! # Inventory
 
-The inventory contains docs for tactics, lemmas, and definitions. These are all disabled
+The inventory contains docs for tactics, lemmas, and definitions. These are all locked
 in the first level and get enabled during the game.
 -/
 
@@ -222,8 +222,11 @@ partial def reprintCore : Syntax → Option Format
 def reprint (stx : Syntax) : Format :=
   reprintCore stx |>.getD ""
 
+/-- A `attr := ...` option for `Statement`. Add attributes to the defined theorem. -/
+syntax statementAttr := "(" &"attr" ":=" Parser.Term.attrInstance,* ")"
+
 /-- Define the statement of the current level. -/
-elab "Statement" statementName:ident ? descr:str ? sig:declSig val:declVal : command => do
+elab "Statement" statementName:ident ? attr:statementAttr ? descr:str ? sig:declSig val:declVal : command => do
   let lvlIdx ← getCurLevelIdx
 
   -- Save the messages before evaluation of the proof.
@@ -485,12 +488,12 @@ elab "MakeGame" : command => do
           return (item, {
             name := item
             displayName := data.displayName
-            category := data.category
-            locked := true })
+            category := data.category })
 
     -- Availability after a given world
     let mut itemsInWorld : HashMap Name (HashMap Name ComputedInventoryItem) := {}
     for (worldId, _) in game.worlds.nodes.toArray do
+      -- Unlock all items from previous worlds
       let mut items := Availability₀
       let predecessors := game.worlds.predecessors worldId
       for predWorldId in predecessors do
@@ -511,16 +514,18 @@ elab "MakeGame" : command => do
       for (levelId, level) in levels do
         let levelInfo := level.getInventory inventoryType
 
-        -- add items in `levelInfo.new` permanently as unlocked
+        -- unlock items that are unlocked in this level
         for item in levelInfo.new do
           let data := (← getInventoryDoc? item inventoryType).get!
           items := items.insert item {
             name := item
             displayName := data.displayName
             category := data.category
+            new := true
             locked := false }
 
-        -- add the statement from the previous level permanently as unlocked
+        -- add the exercise statement from the previous level
+        -- if it was named
         if inventoryType == .Lemma then
           match lemmaStatements.find? (worldId, levelId) with
           | none => pure ()
@@ -530,14 +535,14 @@ elab "MakeGame" : command => do
               name := name
               displayName := data.displayName
               category := data.category
+              new := true
               locked := false }
 
+        -- sort items and disable disabled ones
         let itemsArray := items.toArray
           |>.insertionSort (fun a b => a.1.toString < b.1.toString)
           |>.map (·.2)
           |>.map (fun item => { item with
-            -- if `levelInfo.only` is set, disable everything not in there,
-            -- otherwise disable all in `levelInfo.disabled`
             disabled := if levelInfo.only.size == 0 then
               levelInfo.disabled.contains item.name
             else
diff --git a/server/GameServer/EnvExtensions.lean b/server/GameServer/EnvExtensions.lean
index 927dadb..8c1f9b1 100644
--- a/server/GameServer/EnvExtensions.lean
+++ b/server/GameServer/EnvExtensions.lean
@@ -72,9 +72,11 @@ structure ComputedInventoryItem where
   /-- Category to group inventory items by (currently only used for lemmas). -/
   category : String
   /-- If `true` then the item only gets unlocked in a later level. -/
-  locked : Bool
+  locked := true
   /-- If `true` then the item is blocked for this level. -/
-  disabled : Bool := false
+  disabled := false
+  /-- To mark an item that has been added freshly in this level. -/
+  new := false
 deriving ToJson, FromJson, Repr, Inhabited
 
 /-- Environment extension for inventory documentation. -/