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I am reading this article, however, I am not sure if I've already grasped that article correctly or not, so I really need someone to confirm whether my understanding is correct or not.
Suppose I want to tell everyone a pen belongs to me by saying "これは私のペンです." so just in case I lost it somewhere and someone found it, he will know that pen is mine.
Suppose there are 2 pens on the floor and then I pick mine and say "これがわたしのペンです."
Did I grasp it correctly?
In that linked article there is an example "日本語が上手ですね！" Can I change it using は as in "あなたの日本語は上手ですね！" without changing the meaning?