Change visibility of MoveNextCore to protected

Ix.NET/Source/System.Interactive.Async/AsyncIterator.cs

@@ -77,7 +77,7 @@ namespace System.Linq
                 }
             }
 
-            public abstract Task<bool> MoveNextCore(CancellationToken cancellationToken);
+            protected abstract Task<bool> MoveNextCore(CancellationToken cancellationToken);
 
             public virtual IAsyncEnumerable<TResult> Select<TResult>(Func<TSource, TResult> selector)
             {

Ix.NET/Source/System.Interactive.Async/Select.cs

@@ -106,7 +106,7 @@ namespace System.Linq
                 base.Dispose();
             }
 
-            public override async Task<bool> MoveNextCore(CancellationToken cancellationToken)
+            protected override async Task<bool> MoveNextCore(CancellationToken cancellationToken)
             {
                 switch (state)
                 {

Ix.NET/Source/System.Interactive.Async/Where.cs

@@ -107,7 +107,7 @@ namespace System.Linq
                 base.Dispose();
             }
 
-            public override async Task<bool> MoveNextCore(CancellationToken cancellationToken)
+            protected override async Task<bool> MoveNextCore(CancellationToken cancellationToken)
             {
                 switch (state)
                 {
@@ -180,7 +180,7 @@ namespace System.Linq
                 base.Dispose();
             }
 
-            public override async Task<bool> MoveNextCore(CancellationToken cancellationToken)
+            protected override async Task<bool> MoveNextCore(CancellationToken cancellationToken)
             {
                 switch (state)
                 {