Definition:Strict Positivity Property

From ProofWiki
Jump to: navigation, search


Let $\struct {D, +, \times}$ be an integral domain whose zero is $0_D$.

Let $\struct {D, +, \times}$ be such that a propositional function $P: D \to \set {\mathrm T, \mathrm F}$ can be applied to a subset of $D$ as follows:

\((P \, 1)\)   $:$   Closure under Ring Addition:      \(\displaystyle \forall a, b \in D:\) \(\displaystyle \map P a \land \map P b \implies \map P {a + b} \)             
\((P \, 2)\)   $:$   Closure under Ring Product:      \(\displaystyle \forall a, b \in D:\) \(\displaystyle \map P a \land \map P b \implies \map P {a \times b} \)             
\((P \, 3)\)   $:$   Trichotomy Law:      \(\displaystyle \forall a \in D:\) \(\displaystyle \map P a \lor \map P {-a} \lor a = 0_D \)             
For $P \, 3$, exactly one condition applies for all $a \in D$.             

The propositional function $P$ as defined above is called the strict positivity property.

Also known as

This is usually known in the literature as the positivity property.

However, this is also used to define a similar propositional function, usually defined on a general ring $\struct {R, +, \circ}$ which includes zero in its fiber of truth.

Because $\struct {R, +, \circ}$ may have (proper) zero divisors, $P$ as defined here may not be closed under $\circ$.

Hence it is the intention on $\mathsf{Pr} \infty \mathsf{fWiki}$ to refer consistently to the propositional function as defined on this page as the strict positivity property.

Also see