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It isn't possible to independently verify the chain. This significantly elevates the trust model for checkpoints from choosing among valid chains to trusting that the chain below the checkpoint was valid before being trimmed. Again, tradeoffs....
It is possible but unreasonable because PoW prooves tx history anyway, with relation from current block till genesis.
Possible because i have "not pruned" backup, so if i share it - it will be a natural prove. Isn't it ?