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I am looking at the litecoin code and i cant seem to understand these lines. I am learning to create a new coin.

What exactly is BIP34Height and BIP65Height and BIP66Height?

What is the purpose and what it does to the blocks and what effect it has on mining?

        consensus.BIP34Height = 710000;
        consensus.BIP34Hash = uint256S("f1a13ec4ed9235d9792c581d6549b42340db403e21a16be0a2fe57f7119bc920");
        consensus.BIP65Height = 918684; // bab3041e8977e0dc3eeff63fe707b92bde1dd449d8efafb248c27c8264cc311a
        consensus.BIP66Height = 811879; // 7aceee012833fa8952f8835d8b1b3ae233cd6ab08fdb27a771d2bd7bdc491894
        consensus.powLimit = uint256S("00000fffffffffffffffffffffffffffffffffffffffffffffffffffffffffff");