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24 changes: 12 additions & 12 deletions README.md
Original file line number Diff line number Diff line change
Expand Up @@ -20,19 +20,19 @@ This repository studies a Boolean-indexed polynomial basis in which every basis
Let $N = 2^m$, let $F$ be an arbitrary field, and index Boolean vectors by
$y=(y_0,\ldots,y_{m-1}) \in \{0,1\}^m$. Define

$$
```math
K_y(X)=\prod_{i=0}^{m-1}\left(X^{2^i}+y_i\right).
$$
```

The paper proves three structural facts.

### 1. Boolean kernel basis

The family

$$
```math
\{K_y : y\in\{0,1\}^m\}
$$
```

is a basis of $F[X]_{<N}$, even though every $K_y$ has degree exactly $N-1$.

Expand All @@ -42,15 +42,15 @@ This is deliberately unlike a degree-graded basis: low degree cannot be read off

For

$$
```math
U(X)=\sum_y \lambda_y K_y(X)=\sum_a u_a X^{|a|_2},
$$
```

the monomial coefficients satisfy

$$
```math
u_a=\sum_{y\ge \bar a}\lambda_y.
$$
```

Thus kernel coordinates and monomial coordinates are related by a Boolean zeta transform composed with the complement permutation. The inverse is Boolean Möbius inversion. Both admit $O(N\log N)$ butterfly algorithms.

Expand All @@ -59,21 +59,21 @@ Thus kernel coordinates and monomial coordinates are related by a Boolean zeta t
Split a kernel index as $y=(x,h)$, where $x\in\{0,1\}^k$ and
$h\in\{0,1\}^{q}$ with $q=m-k$. Then

$$
```math
\deg U < 2^k
\quad\Longleftrightarrow\quad
\lambda_{(x,h)}
=
(-1)^{q-\operatorname{wt}(h)}\mu_x
$$
```

for a unique function $\mu:\{0,1\}^k\to F$.

In characteristic two, $-1=1$, so this becomes constancy across each high-coordinate fiber:

$$
```math
\lambda_{(x,h)}=\mu_x.
$$
```

## Why this artifact exists

Expand Down
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