Update documentation

docs/modules/ROOT/nav.adoc

@@ -20,4 +20,4 @@
 
 * xref:utilities.adoc[Utilities]
 
-* xref:knowledge.adoc[Knowledge]
+* xref:fag.adoc[FAQ]

docs/modules/ROOT/pages/faq.adoc

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+Can I restrict a function to EOAs only?
+
+When calling external addresses from your contract it is unsafe to assume that an address is an externally-owned account (EOA) and not a contract. Preventing calls from contracts is highly discouraged. It breaks composability, breaks support for smart wallets like Gnosis Safe, and does not provide security since it can be circumvented by calling from a contract constructor. 
+
+Some criteria to discard an address as a contract address can be:
+
+ - an address with no code
+ - a contract in construction address
+ - an address where a contract will be created
+ - an address where a contract lived, but was destroyed
+
+Furthermore, a contract address can still be considered a contract if the target contract within the same transaction is already scheduled for destruction by `SELFDESTRUCT`, which only has an effect at the end of a transaction.
+Although checking that the address has code, `address.code.length > 0`, may seem to differentiate contracts from EOAs, it can only say that an address is currently a contract, and its negation (that an address is not currently a contract) does not imply that the address is an EOA.
+