Some characters not being read by screen reading software on 3.5.3

[morbidCode]

This is a really small issue. But maybe you'd like to know about it.

Background: I am blind so I am using a screen reading software called JAWS (Job Access with Speech) and NVDA (non-visual desktop access). They are softwares that reads texts from the screen.

Now, in section 3.5.3, there is a procedure called euler-transform. euler-transform has comments. This is how they are being read.

(define (euler-transform s)
(let ((s0 (stream-ref s 0)) ; S question mark question mark ₁
(s1 (stream-ref s 1)) ; S question mark
(s2 (stream-ref s 2))) ; S question mark question mark ₁
(cons-stream
(- s2 (/ (square (- s2 s1))
(+ s0 (* -2 s1) s2)))
(euler-transform (stream-cdr s)))))

I am not sure, but "question mark question mark" doesn't make sense at all. By reading and understanding the code, I think the real characters are:

(let ((s0 (stream-ref s 0)) ; Sn-₁
(s1 (stream-ref s 1)) ; Sn
(s2 (stream-ref s 2))) ; Sn+₁

It's not really a big deel because those are just comments, but I just find it wierd that the characters are being read like that while all the other "+", "-", "n" and even the mathjax rendering are being read correctly. Are these "question mark" type characters being displayed differently?