Yes, but they must go at the top of the file before all your Rules. This error is coming from line 97 which means your lambda is likely after the definition of a Rule or the error is coming from a Rule.
I should note that global lambdas like this are a code smell in Rules DSL. They can be handy in a very small set of circumstances, but they have sever limitations that make them dangerous to use. For example, they are not thread safe. If it gets called twice the variables from the first call will become overwritten by the second call. Also, you cannot call the lambda outside of the .rules file it is defined in. There is almost always a better way. For example: Design Pattern: Separation of Behaviors