instance of general actions

[zhangyuanlin]

I got error message

ErrorID: TYP001
Message: The sort of 
variable [X at (/Users/yuazhang/Desktop/CALM/examples/allInOneMonkeyB.tp :3:53)] 
cannot be determined.
Explanation: Every variable must have a sort from which it obtains its possible values.
Recommendation: Consider adding an instance(Var, sort) literal to the body of the rule.

for ALM statement

            executability conditions
                impossible occurs(X) if
                    instance(X, actions), occurs(Y), X!=Y.

Is there anything wrong here?

[zhangyuanlin]

After adding instance(Y, actions), the error is gone. I am not sure if the current error message is accurate.