Regular value
= Regular value
A value is regular when the derivative is surjective at every point of its preimage.
Every value of a <submersion> is regular, but a map can have some regular values without being a submersion everywhere.
= Regular value
A value is regular when the derivative is surjective at every point of its preimage.
Every value of a <submersion> is regular, but a map can have some regular values without being a submersion everywhere.