Recap of bitcoin so far:
	Signing review
		Encrypt sha256 hash using private key to sign
		Transactions must be signed to be valid

Forming a new block and the bitcoin miner:
	Block includes a hash value for the block
	Must be within a specific range
		Narrower range = more work
		Change the nonce to change the hash value
	So it's a lot of work to produce a valid blockchain!
		This is to prevent an attacker from producing one
	Mining reward:  Special transaction written into the block
		6.25 BTC currently (~$130,000)
		Also receive the transaction fees for the block
		Otherwise, maybe nobody would bother
		As it is, lots of work goes into the blockchain
		Expectation is that eventually transaction fees will be enough

Mining:
	Basically, we guess a bunch of potential nonce values
		The mining pool delivers a range to try
		The miner tries them, and reports the results
			Right away if one works!
			"golden nonce"
		Pool rewards are allocated according to number of nonces tried
	The old days:  Just use a regular computer
		That worked for a while
		Difficulty adjusts for a target time of 10 minutes per block
		Block reward halving (last in May 2020, next in 2024
		Electrical efficiency
			But what if electricity is free, or somebody else is paying?
			malware mining
	Next:  GPU mining
		Some coins can still be mined this way, but not bitcoin
		Lots of ethereum was mined this way until last Fall
		Still profitable for some coins
		A GPU is a lot more flexible
	Even more efficient:  Application-Specific Integrated Circuits
		ASIC only performs one hash function
			A bitcoin miner can't mine all coins
			asicminervalue.com and efficiency, different hash functions
			My miner does sha256, and that's it
		This is where bitcoin is at now, and that's what I brought
		ASIC value, electricity use, and payoff time
			Will it pay off before the difficulty gets too high?
			Or before the next halving?
			Expect profitability to fall off over time
			Let's look at GPU mining too
				whattomine.com
		Note:  Most ASIC miners require 220v
	How much power will it use?
		watts: a rate, how fast we're using power
		watt-hours:  A quantity, how much power we used
			About 10 cents per 1000 watt-hours, or 1 KW/h
		So a 2,000 watt miner would be about 20 cents/hour to run
	What if you were going to use that power anyway?
		To heat your house or something
		A miner is just as efficient as resistance heating!
		Not as efficient as a heat pump
		Heating with gas is cheaper than electricity

What if somebody:
	Doesn't want to use a mining pool?
	Tries to "steal" a golden nonce?
	Decides to cheat by including a different reward transaction?
	Calculates a golden nonce at the same time as somebody else?
	Finds a closed-form calculation for a golden nonce?
	Has lots of solar panels, or a fusion reactor or something?