ch02: new "alice's transaction in a block" figure

ch02.asciidoc

@@ -265,12 +265,12 @@ Jing's winning block became part of the blockchain as block #277316, containing
 You can see the block that includes https://blockchain.info/btc/block/277316[Alice's transaction].
 ====
 
-((("confirmations", "role in transactions")))Approximately 19 minutes later, a new block, #277317, is mined by another miner. Because this new block is built on top of block #277316 that contained Alice's transaction, it added even more computation to the blockchain, thereby strengthening the trust in those transactions. Each block mined on top of the one containing the transaction counts as an additional confirmation for Alice's transaction. As the blocks pile on top of each other, it becomes exponentially harder to reverse the transaction, thereby making it more and more trusted by the network.
+((("confirmations", "role in transactions")))Approximately 20 minutes later, a new block, #277317, is mined by another miner. Because this new block is built on top of block #277316 that contained Alice's transaction, it added even more computation to the blockchain, thereby strengthening the trust in those transactions. Each block mined on top of the one containing the transaction counts as an additional confirmation for Alice's transaction. As the blocks pile on top of each other, it becomes exponentially harder to reverse the transaction, thereby making it more and more trusted by the network.
 
 ((("genesis block")))((("blocks", "genesis block")))((("blockchain (the)", "genesis block")))In the diagram in <<block-alice1>>,  we can see block #277316, which contains Alice's transaction. Below it are 277,316 blocks (including block #0), linked to each other in a chain of blocks (blockchain) all the way back to block #0, known as the _genesis block_. Over time, as the "height" in blocks increases, so does the computation difficulty for each block and the chain as a whole. The blocks mined after the one that contains Alice's transaction act as further assurance, as they pile on more computation in a longer and longer chain. By convention, any block with more than six confirmations is considered irrevocable, because it would require an immense amount of computation to invalidate and recalculate six blocks. We will examine the process of mining and the way it builds trust in more detail in <<mining>>.((("", startref="BToverview02")))((("", startref="MACover02")))
 
 [[block-alice1]]
-.Alice's transaction included in block #277316
+.Alice's transaction included in block #277316 (triangle block)
 image::images/mbc2_0209.png["Alice's transaction included in a block"]
 
 === Spending the Transaction