An isogram is a word that has no duplicate letters. Create a function that takes a string and returns either true or false depending on whether or not it's an "isogram".

Examples

is_isogram("Algorism") ➞ true

is_isogram("PasSword") ➞ false
# Not case sensitive.

is_isogram("Consecutive") ➞ false

Notes

• Ignore letter case (should not be case sensitive).
• All test cases contain valid one word strings.