  
  
  [1XReferences[101X
  
  [[20XFir05[120X]  [16XFirth,  D.[116X,  [17XAn  Algorithm  to  Find Normal Subgroups of a Finitely
  Presented  Group,  up  to  a Given Finite Index[117X, Ph.D. thesis, University of
  Warwick (2005).
  
  
  
  [32X
