[R] set package: more information about syntax

[Jarek Jasiewicz]

Dear All!

I have a few question about proper syntax for fuzzy rules in sets 
package (there is only little help about it):

1) how to use negation (NOT) operator there is only OR (||) in example 
it is NOT, !!, !. I also assume that AND is &&
2) where it can be set. For example:

area %is NOT% large
area %is% NOT large
area %is% !large
etc...

3) how brackets works (as in typical logical operation, are allowed - 
some expert system do not allow use brackets)
Is proper following syntax?

(slope %is% flat && elevation %is% is high) || area %is% large, form 
%is% plateau

Where I can find more information about syntax rules used in that 
(fantastic!) package, except in "Generalised and Customisable Sets in R" 
where is nothing about rules. Maybe rules comes from other, more general 
rule syntax, if yes,I would be grateful for the source

thanks and greetings
Jarek