Pangrama

You work for a company that sells fonts through their website. They'd like to show a different sentence each time someone views a font on their website. To give a comprehensive sense of the font, the random sentences should use all the letters in the English alphabet.

They're running a competition to get suggestions for sentences that they can use. You're in charge of checking the submissions to see if they are valid.

Your task is to figure out if a sentence is a pangram.

A pangram is a sentence using every letter of the alphabet at least once. It is case insensitive, so it doesn't matter if a letter is lower-case (e.g. k) or upper-case (e.g. K).

For this exercise, a sentence is a pangram if it contains each of the 26 letters in the English alphabet.