JESS: Again, newbie's question

[Young-Jin Lee]

Hi, I have a few questions on Jess syntax. First, I don't see any explanation on "(declare)". I assume that it's the same as Lisp's declare, but... Second, what is the "?" in the form? For example, (defrule do-factorial     (need-factorial ?x ?)                              ----     =>     .... ) Does it mean "?" can be bound to anything? Third, the Jess language document briefly explains "backward chaining". Where can I find more example/explanation of backward chaining?   Thanks in advance.   Young-Jin