libbitcoin, interesting I'll have to think about it and look closer at libbitcoin.

but even then there must be some name for the data structure in libbitcoin that maps to the utxo set in core. if utxo set isn't the name for this concept it needs some different name.

"index of the chain" sounds to me suspiciously like utxo set. what are we indexing? i haven't looked yet but i'm guessing txid plus ouput number, ie morally the same as a utxo.

I think my overall point is that we talk about blocks a lot. And we talk about transactions a lot.

But utxo sets are actually the simpler concept, once you know what they are.

Blocks are sort of the means to an end, whereas utxo sets are the end.