User:IssaRice/Logical induction notation

This is in user space because it's not really about machine learning.

Term	Notation	Type	Definition	Notes
${\mathcal {F}}$-combination	$A$	${\mathcal {S}}\cup \{0,1\}\to {\mathcal {F}}_{n}$		Function application of an ${\mathcal {F}}$-combination uses square brackets instead of parentheses. Why? As far as I can tell, this is because each coefficient is in ${\mathcal {F}}$ so is itself a function. This means we have two senses of "application": we can pick out the specific coefficient we want (square brackets), or we can apply each coefficient to return something (parentheses).
Holdings from $T$ against ${\overline {\mathbb {P} }}$ (a $\mathbb {Q}$-combination)	$T({\overline {\mathbb {P} }})$	${\mathcal {S}}\cup \{0,1\}\to \mathbb {Q}$
Trading strategy	$T$	${\mathcal {S}}\cup \{1\}\to {\mathcal {E\!F}}$

Example of a 5-strategy given on p. 18 of the paper:

$\underbrace {\left[(\neg \neg \phi )^{*5}-\phi ^{*5}\right]} _{\xi _{1}}\cdot (\phi -\phi ^{*5})+\underbrace {\left[\phi ^{*5}-(\neg \neg \phi )^{*5}\right]} _{\xi _{2}}\cdot \left(\neg \neg \phi -(\neg \neg \phi )^{*5}\right)$

Since the coefficients ($\xi _{1}$ and $\xi _{2}$) are in ${\mathcal {E\!F}}_{5}$, this is an ${\mathcal {E\!F}}_{5}$-combination. Let's call this 5-strategy $T_{5}$. We can pick out the coefficient for the $\phi$ term like $T_{5}[\phi ]=(\neg \neg \phi )^{*5}-\phi ^{*5}$. But since each coefficient is a feature (which is a function), we can also apply each coefficient to some valuation sequence ${\overline {\mathbb {V} }}$, like this:

$T_{5}({\overline {\mathbb {V} }})=\left[(\neg \neg \phi )^{*5}({\overline {\mathbb {V} }})-\phi ^{*5}({\overline {\mathbb {V} }})\right]\cdot (\phi -\phi ^{*5}({\overline {\mathbb {V} }}))+\left[\phi ^{*5}({\overline {\mathbb {V} }})-(\neg \neg \phi )^{*5}({\overline {\mathbb {V} }})\right]\cdot \left(\neg \neg \phi -(\neg \neg \phi )^{*5}({\overline {\mathbb {V} }})\right)$

Now each coefficient is a real number, so $T_{5}({\overline {\mathbb {V} }})$ is an $\mathbb {R}$-combination. Note that since $T_{5}\colon {\mathcal {S}}\cup \{1\}\to {\mathcal {E\!F}}_{5}$ is a function that takes a sentence or the number $1$ and ${\overline {\mathbb {V} }}$ is a valuation sequence (not a sentence or number), there appears to be a type error in writing $T_{5}({\overline {\mathbb {V} }})$. What is going on is that we aren't evaluating $T_{5}$ at ${\overline {\mathbb {V} }}$; rather, we are evaluating each coefficient of $T_{5}$, to convert the range of $T_{5}$ from ${\mathcal {E\!F}}_{5}$ to $\mathbb {R}$.

To summarize the types:

• $T_{5}\colon {\mathcal {S}}\cup \{1\}\to {\mathcal {E\!F}}_{5}$
• $T_{5}[\phi ]\colon {\mathcal {E\!F}}_{5}$
• $T_{5}({\overline {\mathbb {V} }})\colon {\mathcal {S}}\cup \{1\}\to \mathbb {R}$

External links

• https://arbital.com/p/logical_inductor_nota/
• https://arbital.com/p/logical_induction/