What are the requirements of part performance?

Section 53 A of Transfer of Property Act stipulates certain conditions;
1. It must be contract for transfer of immovable property for consideration.
2. It must be in writing. 
3. It must have been signed by the seller or his authorised agents.
4. The terms of contract shall be clear, should be ascertainable with reasonable care with certainty, the act of part performance should also be part of the contract.
5. The vendor in pursuance of the contract should have put the purchaser in possession of the property. The purchaser should have taken the possession and if already in possession shall continue to be in possession.
6. The purchaser has done some act like payment of consideration in pursuance of the contract or willing to perform his part of contract.