A map 
, where 
is a manifold, is a finite-to-one
factor of a map 
if there exists a continuous surjective map 
such that 
and 
is finite for each 
.
Finite-to-One Factor
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Cite this as:
Weisstein, Eric W. "Finite-to-One Factor." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Finite-to-OneFactor.html