Valuation (measure Theory) - Domain/Measure Theory Definition

Domain/Measure Theory Definition

Let be a topological space: a valuation is any map

satisfying the following three properties


\begin{array}{lll}
v(\varnothing) = 0 & & \scriptstyle{\text{Strictness property}}\\
v(U)\leq v(V) & \mbox{if}~U\subseteq V\quad U,V\in\mathcal{T} & \scriptstyle{\text{Monotonicity property}}\\
v(U\cup V)+ v(U\cap V) = v(U)+v(V) & \forall U,V\in\mathcal{T} & \scriptstyle{\text{Modularity property}}\,
\end{array}

The definition immediately shows the relationship between a valuation and a measure: the properties of the two mathematical object are often very similar if not identical, the only difference being that the domain of a measure is the Borel algebra of the given topological space, while the domain of a valuation is the class of open sets. Further details and references can be found in Alvarez-Manilla et al. 2000 and Goulbault-Larrecq 2002.

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