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diff --git a/Firestore/Source/Core/FSTListenSequence.mm b/Firestore/Source/Core/FSTListenSequence.mm
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+++ b/Firestore/Source/Core/FSTListenSequence.mm
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+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#import "FSTListenSequence.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+#pragma mark - FSTListenSequence
+
+@interface FSTListenSequence () {
+  FSTListenSequenceNumber _previousSequenceNumber;
+}
+
+@end
+
+@implementation FSTListenSequence
+
+#pragma mark - Constructors
+
+- (instancetype)initStartingAfter:(FSTListenSequenceNumber)after {
+  self = [super init];
+  if (self) {
+    _previousSequenceNumber = after;
+  }
+  return self;
+}
+
+#pragma mark - Public methods
+
+- (FSTListenSequenceNumber)next {
+  _previousSequenceNumber++;
+  return _previousSequenceNumber;
+}
+
+@end
+
+NS_ASSUME_NONNULL_END
+\ No newline at end of file