diff --git a/KotlinCore/src/de/steamwar/kotlin/ui/Observer.kt b/KotlinCore/src/de/steamwar/kotlin/ui/Observer.kt
index 8ecb1295..6990e14a 100644
--- a/KotlinCore/src/de/steamwar/kotlin/ui/Observer.kt
+++ b/KotlinCore/src/de/steamwar/kotlin/ui/Observer.kt
@@ -24,9 +24,9 @@ import kotlin.properties.ReadWriteProperty
 import kotlin.reflect.KProperty
 
 abstract class Observable<T> {
-    private val listeners = mutableSetOf<ObserverListener>()
+    internal val listeners = mutableSetOf<ObserverListener>()
 
-    fun removeListener(render: ObserverListener) {
+    open fun removeListener(render: ObserverListener) {
         listeners.remove(render)
     }
 
@@ -46,15 +46,34 @@ abstract class Observable<T> {
             override fun update() = callback(get())
         }
         listeners.add(listener)
+        callback(get())
         return { removeListener(listener) }
     }
 
     abstract fun get(): T
 
-    fun <R> map(mapper: (T) -> R): ReadOnlyProperty<Any?, R> = Delegate(mapper(get()))
+    fun <R> map(mapper: (T) -> R): Observable<R> = Delegate(mapper, this)
 
-    class Delegate<T>(val value: T): ReadOnlyProperty<Any?, T> {
-        override fun getValue(thisRef: Any?, property: KProperty<*>): T = value
+    class Delegate<T, R>(val mapper: (T) -> R, val parent: Observable<T>): Observable<R>(), ReadOnlyProperty<Any?, R> {
+        var value: R? = null
+        var unsubParent = parent.listen {
+            val old = value
+            value = mapper(it)
+            if (old != value) {
+                notifyListeners()
+            }
+        }
+
+        override fun removeListener(render: ObserverListener) {
+            super.removeListener(render)
+            if (listeners.isEmpty()) {
+                unsubParent()
+            }
+        }
+
+        override fun get(): R = value!!
+
+        override fun getValue(thisRef: Any?, property: KProperty<*>): R = value!!
     }
 }