It took me about one week until I realized that I misunderstood the meaning of the expression syntax in the paper. Operator priorities are rediculous!

Let's have a look at the formal expression:

$$ ?x:a \rightarrow b.x\ e $$

At first look, my eyes parsed the expression as:

$$ (?x:a) \rightarrow (b.x) e $$

which is totally WRONG! The correct grouping is

$$ (?x:(a \rightarrow b).x)\ e $$

I really appreciate the great work of the author, but

Please use PARENTHESIS when necessary!