9 question about bitcoin/btc/blockchian

9 Questions about bitcoin

1. how send money to B from A online ?
   A digist signature with A’s private/secrect key(SK).
   B can valide the sign with A’s Public key (PK)
   - compute hash of received content as H1
   - decode signature/fingeprint with A’s PK as H2
   - H1 == H2 ? true : false;
2. how to proof that A no sign this coin/money at history (double spending) without trusted third-party ?
   all pay history is public to everyone(A , B , no trusted third-party).
   check every pay/tx history
   A spend coin/utxo as txi in history tx ? return A(utxo)=>B valid false : compare next his tx.
   after check all his,no return,then return A(utxo)=>B valid true;
3. how to order his tx ?
   - split txs, package tx set to block
4. how to order tx in a block?
   - order by timestamp
5. how to check tx is no modified in a block
   - merkel tree
   - link block with pre block like a chain
6. how to select out pre block?
   - consensus 1,the longest/highest chain’s last block as pre block of will add block
7. who add block is valid?
   - consensus 2,who first find the answer of a question.
8. what is the question ?
   - hash all tx that will be packaged ,out merkel root.
   - find a nonce that combine merkel root and pre block hash(from consensus 1) and other argument , hash then , out H
   - H < curent diffcult nonce?nonce is answer:continue.
9. who has more opportunity to add valid block?
   - compute hash faster / more cpu power
   - lucky