The problem regards the usage of "Indian philosophy" in general. Michel Angot has some interesting pages about it in his Introduction of his translation of the Nyāyabhāṣya (in French, unfortunately). However, the problem is that other labels are also problematic. I try to use "Sanskrit philosophy", but then time and again the term does not work because I want to include also authors who wrote in Prakrit and so on. "Indian" in this sense is only legitimate if conceived as geographically based (a philosophy produced in the Indian subcontinent, including today's Pakistan, Bangladesh, etc.)