Notion of equity under UNFCCC is vague. Why did India want it to be translated into decisions / treaties under Durban Platform?

Equity is a matter of principle that is recognized in the Convention. Its actual significance lies in the fact that the human beings have certain inalienable rights, particularly in regards to the global commons like atmosphere. The definitions of equity can differ but the principle cannot be ignored.
Since the line of differentiation as established under the Convention may be sought to be blurred in any post 2020 arrangement that may also apply to all with varying degree of bindingness, it is important to recognize equity appropriately in formulating this post 2020 dispensation.