its in closure of the operator function!
when you call a number function n at here it returns a function, that cheks if it recives a argument or not,
what if you pass th result of plus function with a value as argument of seven which recives a function?
you have the operation check part with an operation like plus with argument involved in it, l

its hard a little bit , it took me 10 min to undrestand what he did !!!!

undrestanding your solution is like undrestanding the 5th dimention !!!
but i finally figured out what you've did!

i made this with out regex, hahahah !!!! with O(n) loop

am i only stupid one here ???? please dont leave me lone here