A 1-form 
is said to be exact in a region 
if there is a function 
that is defined and of class 
(i.e., is once continuously
differentiable in 
)
and such that 
.
Exact Form
This entry contributed by Andriy Drozdyuk
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Cite this as:
Drozdyuk, Andriy. "Exact Form." From MathWorld--A Wolfram Web Resource, created by Eric W. Weisstein. https://mathworld.wolfram.com/ExactForm.html