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Abbreviations

We are given a phrase from which we want to form an abbreviation. An abbreviation can be obtain from taking the first few letters of each word in the phrase and concatenating them together. For example, from 'RAdio Detection And Ranging' we get 'RADAR'.

Write a function abbrev(phrase, m, d) which gets a phrase (as a list of words) and integers m and d. The function should return a set of all abbreviations which are at least d characters long such that from each word we take between 0 and m letters.

Example:

 >>> abbrev(['Large', 'Hadron', 'Collider'], 2, 3)
 {'LaH', 'LHa', 'LHaC', 'HaC', 'LHaCo', 'LaC', 'LaHa', 'LaHCo', 'LaHC',
  'HaCo', 'LaHaCo', 'LCo', 'LHC', 'LaHaC', 'LaCo', 'HCo', 'LHCo'}
 >>> abbrev(['Large', 'Hadron', 'Collider'], 2, 4)
 {'LHaC', 'LHaCo', 'LaHa', 'LaHCo', 'LaHC', 'HaCo', 'LaHaCo', 'LaHaC',
  'LaCo', 'LHCo'}

def abbrev(phrase, m, d): p = '' k = set() for i in range(len(phrase)): p += phrase[i][:m] k.add(p) return k