One of the Eilenberg-Steenrod axioms. Let 
be a single point space. 
unless 
, in which case 
where 
are some groups. The 
are called the coefficients
of the homology 
.
Dimension Axiom
See also
Eilenberg-Steenrod Axioms, HomologyExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Dimension Axiom." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/DimensionAxiom.html