Paper I visual guide · Visual 17 of 22 · COORDINATE ALGEBRA / NORMAL FORM RATHER THAN A CURVE SKETCH

A relation becomes a packet product rule

Main text: Worked coordinate ring model. Normal form and exact multiplication

Start reading

Resources & source

Original plate in the monograph PDF · Original atlas source

Skip contents and start reading

Work over \({\mathbb Q}\) in

\[ A={\mathbb Q}[x,y]/(y^2-x^3+x). \]

Because the relation is monic of degree two in \(y\), each element has one unique form \(a(x)+yb(x)\). The two packet coefficients are polynomials, not scalars.

Two coefficient lanes in a coordinate ring
Original drawing. Read the description below; expand the labels and data for selectable text.

Reading the drawing

Two rows retain independent polynomial coefficient slots for a(x) and b(x). The final relation rewrites higher powers of y into these lanes rather than discarding them.

Drawing labels and data 14 labels

Read the original labels as selectable text. Tables preserve grid relationships; other short labels are grouped compactly.

  • \(1\)
  • \(x\)
  • \(x^2\)
  • \(x^3\)
  • \(x^4\)
  • \(\cdots\)
  • \(y\)
  • \(xy\)
  • \(x^2y\)
  • \(x^3y\)
  • \(x^4y\)
  • \(\cdots\)
  • Independent coefficient slots: \(a(x)\) and \(b(x)\)
\[y^2=x^3-x\quad\Longrightarrow\quad y^3=(x^3-x)y\]

Open the full-size drawing

Evidence note from the source edition

A finite window of the two infinite coefficient lanes. Higher powers of \(y\) are rewritten using the relation. They are not simply discarded. No geometric genus or smoothness claim is encoded by this picture.

Multiplication by \(y\) transfers between the lanes

In the ordered coefficient coordinates \((a,b)\),

\[ M_y={\begin{pmatrix}0&x^3-x\\1&0\end{pmatrix}},\qquad M_y^2=(x^3-x)I. \]

The entries denote multiplication maps on \({\mathbb Q}[x]\). For \(f=a_0+ya_1\) and \(g=b_0+yb_1\),

\[ fg=\bigl(a_0b_0+(x^3-x)a_1b_1\bigr) +y\bigl(a_0b_1+a_1b_0\bigr). \]

In particular,

\[ (x^2+y)(x-y)=x+(x-x^2)y. \]

One module seed does not mean one algebra generator

Starting from \(1\), the fixed multiplication operators \(M_x,M_y\) generate every monomial in normal form. Thus the algebra is cyclic as a module over its multiplication algebra. This does not remove either address operator, and does not say that the algebra is generated by one algebra element.

Read this as

The relation controls an exact weighted transfer between coefficient lanes. Packet reconstruction is \(a+yb\), while packet multiplication retains the weight \(x^3-x\).

Source and conversion record

The original atlas wording, equations, and drawing labels are retained. Drawings are views of the retained monograph PDF. Text descriptions and table headings are added reading aids. This conversion does not rebuild TeX, rerun the examples, audit proofs or compile Lean.

Conversion checks and source hashes

Notation in Paper I

Look up a symbol without leaving this chapter. Select text before opening help to search for it.

Search this work’s notation.

    Symbols can have different meanings in different passages. Read each result in its own context.

    Open the full notation index