Notice from the semantics and from the implementation of the let expression that Varlang doesn’t place any restriction on defining the same variable two or more times in the same let expression. In fact, a variable can be defined any number of times, and only the rightmost definition would have an effect in the body of the let expression. So the program (let ((a 3) (a 4) (a 2) (a 342)) a) would give the answer 342. Modify the semantics of the Varlang programming language so that all variable names defined in a let expression must be unique.