Comments about flat-fee costs.

gas.md

@@ -479,7 +479,9 @@ not include the code loading cost.
 
 Also, it may seem counterintuitive to pay for the code loading cost, one may
 expect to pay a flat fee as in the EVM model. A flat fee is usually less
-efficient, so we're using a size-based fee.
+efficient, so we're using a size-based fee. There is a similar memory
+consumption associated with loading the code which, arguably, might be included
+in a flat-fee cost.
 
   ```hs
   -- CALLOP in [CALL, CALLCODE, DELEGATECALL, STATICCALL]
@@ -537,6 +539,10 @@ efficient, so we're using a size-based fee.
   memorySizeCallee(existent-account-success) = callDataSize
   ```
 
+  The calee starts with a memory usage of memorySizeCallee (absolute, not a
+  delta). There is a free memory allowance for each new contract call, equal to
+  the maximum EVM stack size, that will be taken into account separately.
+
   `constantMemorySize` is the size of whatever is part of the saved state
   except for the code and callData (calldepth, callValue, id, gas, caller,
   static)