Decoding Occupation Contract Terms: Section 168 and 170

Please explain this term in an occupation contract: 

"The landlord may not give the contract-holder a possession notice specifying the ground in section 170 of the Act after the end of the period of two months starting with the date specified in the notice under section 168 of the Act (contract-holder's notice) as the date on which the contract holder would give up possession of the dwelling."

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Contract-holder's Notice

A contract-holder may end the occupation contract at any timeĀ before the earlierĀ of the landlord giving the written statement, or the occupation date.