A pseudonym or alias is a name adopted by a person for a particular purpose, which differs from his or her true name. A pseudonym may be used by social activists or politicians for political purposes or by others for religious purposes. It may be a soldier's nom de guerre¹ or an author's nom de plume². It may be a performer's stage name³ or an alias used by visual artists, athletes, fashion designers, or criminals. Pseudonyms are occasionally used in fiction such as by superheroes or other fictional characters.

For example, what are the more familiar pseudonyms of the following people?

1. Georgios Kyriacos Panayiotou

2. Margaretha Geertruida Zelle MacLeod

3. Ioseb Vissarionovich Dzhugashvili

4. Cassius Marcellus Clay Jr.

5. Choo Yeang Keat

Assignment

A pseudonym is often used to mask the identity of a person. However, we can also use a (secret) keyword to make the real name of the person unrecognizable.

For example, suppose we use GEORGEMICHAEL as a keyword to mix the letters of the alphabet in the following way. First we write down the letters of the keyword, where letters that occur more than once are only written upon their first occurrence (indicated in green below). Then we write down all remaining letters in the order in which they appear in the alphabet (indicated in orange below).

This creates a permutation of the letters of the alphabet that can be used to decode messages. Each occurrence of the first letter in the alphabet is replaced by the first letter in the permutation, the second letter in the alphabet by the second letter of the permutation, and so on.

Below you can see for example how the message GEORGIOSKYRIACOSPANAYIOTOU is encoded into CMKQCAKSBYQAGOKSNGJGYAKTKU using GEORGEMICHAEL as a keyword.

When decoding, the roles of the alphabet and the permutation are reversed: the first letter in the permutation is replaced by the first letter in the alphabet, the second letter in the permutation by the second letter in the alphabet, and so on.

Your task:

• Write a function permutation that takes a keyword (str). The function must return the permutation of the alphabet (str, in uppercase) obtained from the given keyword. The function must only take into account the letters in the given keywords. Any character in the keyword that is no letter must be ignored. Moreover, no distinction may be made between uppercase and lowercase letters.

• Write a function encode that takes a message (str) and a keyword (str). The function must return the encoded version of the given message, based on the given keyword. This is done by replacing uppercase letters by their corresponding uppercase letter, and replacing lowercase letters by their corresponding lowercase letter. Characters in the given message that are no letter simply remain in place in the encoded message.

• Write a function decode that takes an encoded message (str) and a keyword (str). The given message has been encoded based on the given keyword (see function encode). The function must return the original version of the message.

Example

>>> permutation('George Michael')
'GEORMICHALBDFJKNPQSTUVWXYZ'
>>> permutation('Mata Hari')
'MATHRIBCDEFGJKLNOPQSUVWXYZ'
>>> permutation('Joseph Stalin')
'JOSEPHTALINBCDFGKMQRUVWXYZ'
>>> permutation('Muhammad Ali')
'MUHADLIBCEFGJKNOPQRSTVWXYZ'
>>> permutation('Jimmy Choo')
'JIMYCHOABDEFGKLNPQRSTUVWXZ'

>>> encode('Georgios Kyriacos Panayiotou', 'George Michael')
'Cmkqcaks Byqagoks Ngjgyaktku'
>>> encode('Margaretha Geertruida Zelle MacLeod', 'Mata Hari')
'Jmpbmprscm Brrpspudhm Zrggr JmtGrlh'
>>> encode('Ioseb Vissarionovich Dzhugashvili', 'Joseph Stalin')
'Lfqpo Vlqqjmlfdfvlsa Ezautjqavlbl'
>>> encode('Cassius Marcellus Clay Jr.', 'Muhammad Ali')
'Hmrrctr Jmqhdggtr Hgmy Eq.'
>>> encode('Choo Yeang Keat', 'Jimmy Choo')
'Mall Xcjko Ecjs'

>>> decode('Cmkqcaks Byqagoks Ngjgyaktku', 'George Michael')
'Georgios Kyriacos Panayiotou'
>>> decode('Jmpbmprscm Brrpspudhm Zrggr JmtGrlh', 'Mata Hari')
'Margaretha Geertruida Zelle MacLeod'
>>> decode('Lfqpo Vlqqjmlfdfvlsa Ezautjqavlbl', 'Joseph Stalin')
'Ioseb Vissarionovich Dzhugashvili'
>>> decode('Hmrrctr Jmqhdggtr Hgmy Eq.', 'Muhammad Ali')
'Cassius Marcellus Clay Jr.'
>>> decode('Mall Xcjko Ecjs', 'Jimmy Choo')
'Choo Yeang Keat'