Paragraph on proof checking ; fixes MinaProtocol#6

MIPS/mip-zkapps.md

@@ -20,12 +20,12 @@ The zkApps protocol aims to add a smart contract layer to Mina which extends the
 
 
   **General programmability** - able to execute and settle arbitrary programs, not constrained to a particular VM model, but instead flexibly designed to support any number of execution models, VM-like or otherwise
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+
   **Programmable privacy** - the privacy of both inputs to smart contracts and their state can be programmed by their developers
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+
   **Constant in verification time** - individual transactions are executed, or more accurately “proven” asynchronously off-chain and verified on chain in constant time, independent of computational complexity
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 This MIP represents the first iteration of such a protocol.
 
 ## Specification
@@ -424,6 +424,14 @@ the second pass does not change the result from the first pass.
 The first-pass processing is identical to what it was in the protocol
 before the changes proposed in this document.
 
+Proofs inside of account updates are checked when zkApp transactions are
+added to the transaction pool against some potential verification key
+(depending on how subsequent transactions are ordered; see DDOS mitigations for
+more details on this). When a block is created, the proofs are not re-checked
+because they were already checked when added to the pool. When a block is
+received, all checks required to verify that the sender doesn't lie are
+re-verified, but the proof is not explicitly checked in all cases.
+
 #### Transaction Application
 
 If the zkApp succeeds, the balance changes from all the account