 
 extension RxAssertion {
   public func not() -> RxAssertion<O> {
-    var copy = self
-    copy.isNot = !self.isNot
-    return copy
+    self.isNot = !self.isNot
+    return self
   }
 }
 


extension RxAssertion {
  public func within(_ timeRange: Range<TestTime>) -> RxAssertion<O> {
    var copy = self
    copy.timeRange = timeRange
    return copy
  }

  public func since(_ timeSince: TestTime) -> RxAssertion<O> {


extension RxAssertion {
  public func filterNext() -> RxAssertion<O> {
    self.shouldFilterNext = true
    return self
  }
}

