A submersion is a smooth map 
when
 |
given that the differential, or Jacobian, is surjective at every 
in 
.
The basic example of a submersion is the canonical submersion 
of 
onto 
when 
,
 |
In fact, if 
is a submersion, then it is possible to find coordinates around 
in 
and coordinates around 
in 
such that 
is the canonical submersion written in these coordinates.
For example, consider the submersion of 
onto the circle 
, given by 
.
