Hi,
the problem is in rule:
if (chestpain is ASYMPTOMATIC or restpress is MAX or serum is MAXLEVEL) and (smoke is LOWPOSSIBILITY or sugar is LEVELNO or minrate is MINRATE or restrate is HIGHRATE) then angin is MASSIVE
where you refer to minrate, but you have not added any variable named minrate to the engine.
In addition, please make sure you have considered the precedence order of the connectors and|or in your rules. If unsure, please group propositions in parenthesis as I have done (if that grouping makes sense to your problem).
Notice also that since you are using and|or in your rules, you have to set the respective conjunction and disjunction operators of your choice. For example,
engine.configure("AlgebraicProduct", "AlgebraicSum", "AlgebraicProduct", "AlgebraicSum", "Centroid");
Cheers.
