[C# Python Java] is operator, instanceof operator

[Python] is operator, is not operator

https://www.geeksforgeeks.org/difference-operator-python/

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[C#] is operator, as operator

https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/is

https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/as

https://www.geeksforgeeks.org/c-sharp-is-operator-keyword/

https://www.geeksforgeeks.org/c-sharp-as-operator-keyword/

https://www.geeksforgeeks.org/is-vs-as-operator-keyword-in-c-sharp/

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[C++/CLI]

https://docs.microsoft.com/en-us/cpp/dotnet/interoperability-with-other-dotnet-languages-cpp-cli?view=vs-2019#implement_isas

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[Java] instanceof operator

https://www.javatpoint.com/downcasting-with-instanceof-operator

https://www.baeldung.com/java-instanceof