Most Wanted Letter Most Wanted Letter
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You are given a text, which contains different English letters and punctuation marks. You should find the most frequent letter in the text. The letter returned must be in lowercase.
During the search for the most wanted letter, casing doesn’t matter, "A" == "a". Make sure you don’t count in the punctuation marks, digits and whitespaces, just letters.

If you have two or more letters occurring the same number of times, then return all of them as a list. For example -- "Hello, Evan" should return ['e', 'l'].

Input: A text for analysis as a string.

Output: The list of the most frequent letters in lowercase.

Example:

most_wanted("Hello World!") == ["l"]
most_wanted("How do you do?") == ["o"]
most_wanted("One") == ["o", "n", "e"]
most_wanted("Oops!") == ["o"]
most_wanted("AAaooo!!!!") == ["a", "o"]
most_wanted("abe") == ["a", "b", "e"]

How it is used: For most decryption tasks you need to know the occurrence frequency of various letters in a section of text. For example: we can easily crack a simple addition or substitution cipher if we know the frequency in which letters appear. It’s pretty interesting stuff for language experts!

Precondition:
A text contains only ASCII symbols.
0 < len(text) ≤ 105