Pangram checker

You are encouraged to solve this task according to the task description, using any language you may know.
A pangram is a sentence that contains all the letters of the English alphabet at least once.

For example:   The quick brown fox jumps over the lazy dog.



Task

Write a function or method to check a sentence to see if it is a   pangram   (or not)   and show its use.



Related tasks

   determine if a string has all the same characters
   determine if a string has all unique characters


proc pangram? {sentence} {
    set letters [regexp -all -inline {[a-z]} [string tolower $sentence]]
    expr {
        [llength [lsort -unique $letters]] == 26
    }
}
puts [pangram? "This is a sentence"];  # ==> false
puts [pangram? "The quick brown fox jumps over the lazy dog."]; # ==> true