CH01::BGP: clarify problem; drop "widde applicability"

- A key element of the problem is *leaderless* selection; mention this.

- Drop the list of other things PoW helps with.  Some of them are very
  wrong, e.g. "proving the fairness of elections".

ch01.asciidoc

@@ -131,15 +131,12 @@ Satoshi Nakamoto withdrew from the public in April 2011, leaving the responsibil
 ((("Byzantine Generals' Problem")))Satoshi Nakamoto's invention is
 also a practical and novel solution to a problem in distributed
 computing, known as the "Byzantine Generals' Problem." Briefly, the
-problem consists of trying to agree on a course of action or the state
-of a system by exchanging information over an unreliable and potentially
-compromised network. ((("central trusted authority")))Satoshi Nakamoto's
-solution, which uses the concept of Proof-of-Work to achieve consensus
-_without a central trusted authority_, represents a breakthrough in
-distributed computing and has wide applicability beyond currency. It can
-be used to achieve consensus on decentralized networks to prove the
-fairness of elections, lotteries, asset registries, digital
-notarization, and more.
+problem consists of trying to get multiple participants without a leader
+to agree on a course of action by exchanging information over an
+unreliable and potentially compromised network. ((("central trusted
+authority")))Satoshi Nakamoto's solution, which uses the concept of
+Proof-of-Work to achieve consensus _without a central trusted
+authority_, represents a breakthrough in distributed computing.
 ****