Undefined Identifier for a string in Scheme

Question

I have the following function below that I am trying to define, but for some reason it does not work, I get the error. On a side note, i am using Dr. Racket for this project.

“low: undefined; cannot reference undefined identifier"

this is the function that I have defined

> (define (frequency amtFrequency)
    (cond
        ((<= amtFrequency 30)“Very Low Frequency”)
        ((<= amtFrequency 300)“Low Frequncy”)
        ((<= amtFrequency 3000)“Medium Frequency”)
        ((<= amtFrequency 30000)“High Frequency”)
        ((<= amtFrequency 328600)“Very High Frequency”)
        (t# “Ultrahigh Frequency”)
    )
)
> (frequency 35)

. . “low: undefined;
 cannot reference undefined identifier
> 

Answer 1

It's a text-formatting problem, you probably copied the code from some poorly typeset source, or the code was written in a text editor other than DrRacket's. Just replace “...” with "...". Also, it's recommended to use else and not #t for the last condition. This should work:

(define (frequency amtFrequency)
  (cond
    ((<= amtFrequency 30)      "Very Low Frequency")
    ((<= amtFrequency 300)          "Low Frequency")
    ((<= amtFrequency 3000)      "Medium Frequency")
    ((<= amtFrequency 30000)       "High Frequency")
    ((<= amtFrequency 328600) "Very High Frequency")
    (else                     "Ultrahigh Frequency")))