RE: [Core] updated safeness condition

> how about:
> "Intuitively, safeness of rules guarantees that when performing
> reasoning in a forward-chaining manner, it is possible to find
bindings
> for all the variables in the rule before it is "fired"."
> 

I would replace the last sentence by this:

"it is required that all the variables in the rule condition part be
bound."

Changhai