class_docstr: Helper data object for training IBM Models 3 and up
  
  Read-only. For a source sentence and its counterpart in the target
  language, this class holds information about the sentence pair's
  alignment, cepts, and fertility.
  
  Warning: Alignments are one-indexed here, in contrast to
  nltk.translate.Alignment and AlignedSent, which are zero-indexed
  This class is not meant to be used outside of IBM models.
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docstr: :return: Whether the word in position ``j`` of the target
      sentence is a head word
docstr_tok: [":","return",":","Whether","the","word","in","position","``","j","``","of","the","target","sentence","is","a","head","word"]
code: def is_head_word(self, j):
      """
      :return: Whether the word in position ``j`` of the target
          sentence is a head word
      """
      i = self.alignment[j]
      return self.cepts[i][0] == j
  
imports: from bisect import insort_left
  from collections import defaultdict
  from copy import deepcopy
  from math import ceil
label_desc: Use image node_id 3 for calling the AlignmentInfo obj's underlying member method code with example usage: obj.is_head_word(j) and returns: unknown