The ref project can't be packed

Ix.NET/Source/System.Interactive/Skip.cs

@@ -8,6 +8,7 @@ namespace System.Linq
 {
     public static partial class EnumerableEx
     {
+#if !(REF_ASSM && NETCOREAPP2_0)
         /// <summary>
         ///     Bypasses a specified number of contiguous elements from the end of the sequence and returns the remaining elements.
         /// </summary>
@@ -32,6 +33,7 @@ namespace System.Linq
 
             return source.SkipLast_(count);
         }
+#endif
 
         private static IEnumerable<TSource> SkipLast_<TSource>(this IEnumerable<TSource> source, int count)
         {
@@ -47,4 +49,4 @@ namespace System.Linq
             }
         }
     }
-}
+}

Ix.NET/Source/System.Interactive/Take.cs

@@ -8,6 +8,7 @@ namespace System.Linq
 {
     public static partial class EnumerableEx
     {
+#if !(REF_ASSM && NETCOREAPP2_0)
         /// <summary>
         ///     Returns a specified number of contiguous elements from the end of the sequence.
         /// </summary>
@@ -29,6 +30,7 @@ namespace System.Linq
 
             return source.TakeLast_(count);
         }
+#endif
 
         private static IEnumerable<TSource> TakeLast_<TSource>(this IEnumerable<TSource> source, int count)
         {
@@ -55,4 +57,4 @@ namespace System.Linq
             }
         }
     }
-}
+}

Ix.NET/Source/refs/System.Interactive/System.Interactive.csproj

@@ -9,6 +9,7 @@
     <DefineConstants>$(DefineConstants);REF_ASSM</DefineConstants>
     <ProduceReferenceAssembly>true</ProduceReferenceAssembly>
     <Deterministic>true</Deterministic>
+    <IsPackable>false</IsPackable>
   </PropertyGroup>
 
   <ItemGroup>