Specify no need to store equivocating messages.

FIPS/fip-0086.md

@@ -294,7 +294,7 @@ The receiver of a message only considers messages with valid signatures and disc
 
 Two (or more) messages $m1$ and $m2$ are called _equivocating messages_ if $m1.Sender=m2.Sender \land m1.Instance=m2.Instance \land m1.Value ≠ m2.Value \land m1.MsgType=m2.MsgType \land \texttt(if applicable)\ m1.Round=m2.Round$. We call $m1.Sender$ an _equivocating sender_.
 
-A set of messages $M$ that does not contain equivocating messages is called _clean_. Participants discard all equivocating messages when forming clean sets.
+A set of messages $M$ that does not contain equivocating messages is called _clean_. Participants discard all equivocating messages when forming clean sets. In fact, in the proposed version of GossiPBFT in this document, only one of the equivocating messages needs to be stored (thanks to evidences explicitly validating a message).
 
 
 #### Predicates and functions used in the protocol