On Regular Mac Lane-Vaquié chains
Let $(K^h,v^h)$ be a Henselization of a valued field $(K,v)$, $μ$ any extension of $v$ to $K[x]$, and $μ^h$ the canonical extension of $μ$ and $v^h$ to $K^h[x].$ In this paper, we study two new invariants associated with a Mac Lane-Vaquié chain (MLV) of $μ$, namely, the defect of each augmentation step and the regularity of an MLV chain of $μ$. This, in turn, extends the notion of regularity of a complete sequence of abstract key polynomials for $μ$ to the regularity of $μ$ itself. We also prove that the regularity of $μ$ is a sufficient condition for the equality of the depths of $μ$ and $μ^h$. Furthermore, it is a necessary and sufficient condition for the equality of the defect and relative gap of each augmentation step of an MLV chain of $μ.$ Finally, we show that if $μ$ has finite degree, then the regularity of $μ$ is equivalent to $ \operatorname{deg}(μ)=\operatorname{deg}(μ^h)$.