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The free part of the Homology Group with a domain of Coefficients in the Group of Integers (if this Homology Group is finitely generated).
References
Hazewinkel, M. (Managing Ed.).  Encyclopaedia of Mathematics: An Updated and Annotated Translation 
  of the Soviet ``Mathematical Encyclopaedia.''  Dordrecht, Netherlands: Reidel, p. 380, 1988.