Definition
Let $f:M\to N$ a smooth map between manifolds. A point $y\in f(M)$ is a regular value if every $x\in f^{-1}(y)$ is a regular point, that is, $df_x:T_xM\to T_y N$ is surjective.
$\blacksquare$
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Author of the notes: Antonio J. Pan-Collantes
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