Lambda Notation

λambda notation — how symbols render, everywhere

The concern this skill owns is rendering, not subject content: the mechanical rules that make math, prose, and callouts render cleanly in the LambdaMind panes, Obsidian, and terminals. Every quantitative field skill loads this, so the discipline is written once and inherited — never copied into a subject skill.

Inline and display math

• Inline $…$. No space just inside the delimiters: $x^2$, never $ x^2 $. A dollar sign meant as currency is escaped: \$150, \$1.20 — an unescaped $…$ around prose renders the prose as broken math.
• Display $$…$$. A blank line before and after the block (the $$ blank-line rule); a $$ jammed against text on either side fails to render as a block.
• No bare underscores in prose. a_i outside math becomes italics soup — keep subscripts inside $…$ ($a_i$), or write them out in words.
• < inside math is a card/line-eating trap. \(p<N\) can be parsed as an opening tag and swallow everything to the next >. Write p < N with a space, or \lt, when the render target is HTML-ish (Anki cards especially).

Where each form is allowed

• File output (session files, the worksheet, atoms, cards): LaTeX that the vault renderer shows — $…$, $$…$$, \(…\)/\[…\] per SPEC schema 1. The session file is the source of truth and must read cleanly on its own.
• Terminal / chat prose with no math renderer: use unicode math (K = Σ⁻¹, ∑, √, ≤), not raw LaTeX — raw $\Sigma^{-1}$ in a plain terminal is noise. On agents without a math renderer, restated MCQ options are compact unicode.
• Restate answers self-contained: Correct: **(b)** $h = \Sigma^{-1}\mu$, never a dangling letter.

Callout hygiene

Every line of a callout — including the [!type] title — starts with > ; a bare [!warning] renders as literal text. Re-emit the whole callout with prefixes intact when replacing a checkbox block with a verdict.

Prose conventions (house style)

• Acronyms expand on first use in any session document: "graph neural network (GNN)" first, bare GNN after. Files are re-read cold.
• No emoji, ever — session files, DAG files, chat. Classical print: typographic glyphs only — ✓ ✗ → ⇒ · § ¶ † ☞ (the manicule ☞ is the "see slides/reading" pointer). Colour emoji are vetoed on sight.

Figures and charts

Notation is text; figures are not. For any diagram, plot, or chart — including the mermaid xychart-beta traps and the TikZ compile-verify loop — use the lambda-draw skill. Do not restate its rules here.