The alphabet has 26 letters, whereas the keypad of a mobile phone or GPS device usually has far less keys. The multi-tap technique was one of the first methods used to enter text messages on such devices.

The idea is quite simple: the letters of the alphabet are printed in groups of three or four under each key, beginning on the 2-key (2=ABC, 3=DEF, 4=GHI, 5=JKL, 6=MNO, 7=PQRS, 8=TUV, 9=WXYZ). The technique is then used by repeatedly pressing the same key to cycle through the letters corresponding to that key. In order to enter the letter A, for example, the 2-key must be pressed once. If you want to enter the letter B, the same key must be pressed twice. Pausing for a set period of time will automatically choose the current letter in the cycle, as will pressing a different key. This allows to enter two letters that are mapped on the same key.

The T9 technique is an improvement over the multi-tap technique, originally developed by Tegic Communications. The name of the technique stands for Text on 9 keys, and it is a patented predictive text technology for mobile phones. T9 allows words to be entered by a single keystroke for each letter, as opposed to the multi-tap approach used in conventional phone text entry. For example, the word Banner can be entered with the following sequence of keystrokes: 2 (ABC), 2 (ABC), 6 (MNO), 6 (MNO), 3 (DEF) and 7 (PQRS). The T9 system looks up all possible words corresponding to the sequence of keystrokes in a built-in dictionary. If there are multiple possibilities, the user needs to select the intended word from a list. This usually works a lot faster than entering the individual letters using multi-tap. Two words corresponding to the same sequence of keystrokes with the T9 technique are called mobile synonyms.

Assignment

• Write a function T9 that takes a single string containing letters only. The function must return the sequence of keystrokes that needs to be entered on a mobile phone keypad supporting T9 in order to enter the given word. The function should handle the given word case-insensitively.

• Use the function T9 to write a function mobileSynonyms that takes two string arguments representing words that contain letters only. The function must return a Boolean value that indicates whether or not the two given words are mobile synonyms.

Example

>>> T9('Banner')
'226637'
>>> T9('succes')
'782237'
>>> T9('rubber')
'782237'

>>> mobileSynonyms('succes', 'rubber')
True
>>> mobileSynonyms('Monday', 'Friday')
False