Consider the following statements about Bhai Kahn Singh Nabha:

1. He authored Mahan Kosh, the first encyclopedia of Sikh literature.
2. His book Ham Hindu Nahin clearly defined Sikh identity as distinct from Hinduism.
3. He was a judge in the Patiala High Court.
4. His work Gurmat Prabhakar focuses on Sikh philosophy and religious concepts.

Which of the above statements are correct?