Definition:Submersion
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Definition
Let $X$ and $Y$ be manifolds, with $\dim X \ge \dim Y$.
Let $f: X \to Y$ be smooth and $f \left({x}\right) = y$.
Let $df_x: T_x \left({X}\right) \to T_y \left({Y}\right)$ be a surjection.
Then $f$ is called a submersion of $X$ on $Y$.
The context of $df_x: T_x \left({X}\right) \to T_y \left({Y}\right)$.
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