Stable lower estimates for smooth mappings and for gradients of smooth function

In this article is discussed a stable lower estimate for gradients of functions near a critical point. It is stable in the sense that if the function belongs to a family of functions depending smoothly on a finite-dimensional parameter, then the estimate will be correct for functions with close parameter values. Related to this estimate is a stratification of the space of jets of functions; the strata are semialgebraic sets of increasing codimension.
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