Arithma

A computer algebra system written in Rust. Exact arithmetic, not floating-point approximation. LaTeX in, LaTeX out. Works as a CLI tool for humans and as an MCP server for AI agents.

Arithma exists because mathematics tools should be correct. Not approximately correct, not usually correct, but correct in the way that exact rational arithmetic and well-chosen algorithms make possible.

Why Arithma

Single binary, no dependencies. The MCP server is a 3.3 MB binary. No Python runtime, no Java, no Wolfram kernel, no network calls. Copy it anywhere and it works.

Exact arithmetic. Every computation uses rational numbers (BigRational), not floating-point. $\frac{1}{3} + \frac{1}{3} + \frac{1}{3} = 1$, not 0.9999999999999998. Results are deterministic and reproducible.

Silence over lies. If Arithma cannot compute something, it says so. It never guesses, approximates heuristically, or returns an unverified result. An agent that gets "I can't do this" can try a different approach. An agent that gets a wrong answer propagates it through its entire reasoning chain.

Proves what's impossible. The Risch algorithm doesn't just integrate — it can prove when no elementary antiderivative exists. Ask for $\int e^{-x^2},dx$ and you get a mathematically rigorous explanation of why no closed form exists, not silence or a wrong answer. And when the antiderivative is a known special function, the impossibility result names it: $\int e^{-x^2},dx = \tfrac{\sqrt{\pi}}{2},\mathrm{erf}(x)$ — the theorem ("not elementary") and the answer beyond it, together. Recognition covers erf, Ei, and li, each guarded by a differentiation round-trip; an unrecognized integrand keeps the bare certificate rather than a guessed name.

Every answer declares its evidence. Each MCP response carries a result_status: exact (decision procedure), verified (numeric agreement at n points — evidence, never proof), approximate (floating-point result with a first-order propagated error bound and a significant_digits count), heuristic, unable_to_compute, or provably_impossible (with certificate). An agent can tell an algebraic identity from "agreed at 12 test points" — because those are different things. Every caveat carries a machine-readable code from a fixed registry (the prose message carries no contract), every refusal states its reason as a code, and bounded numeric outcomes publish the error_bound they were judged against. Verdict-shaped tools additionally carry a machine-readable verdict (pass/fail/inconclusive) — no consumer ever parses prose to learn an outcome. result_status is emitted both as a top-level field and inside structuredContent, so typed SDK clients that drop unknown siblings still see it. See docs/result-status.md.

Verifies whole derivations, not just answers. The verify_chain tool takes an ordered list of reasoning steps — each declaring its relation to the previous one (equals, derivative_of, integral_of, substitution, implies, solution_of, factored_form_of) — and checks every step by the mechanism appropriate to its relation. The chain's status is the minimum evidence across steps: one numeric step makes the whole chain verified, never exact. A failing step carries the specific counterexample that refutes it. The counterexample is the diagnosis.

1813 tests, zero failures. Every algorithm is verified against known results. The simplifier has a verified idempotency contract: simplify(simplify(e)) = simplify(e).

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Capabilities

Algebra & Simplification

Feature	Example
Polynomial factoring (Berlekamp-Zassenhaus)	$x^4-1 \to (x+1)(x-1)(x^2+1)$
Radical simplification	$\sqrt{12} \to 2\sqrt{3}$, $\sqrt{4a^2} \to 2\lvert a\rvert$
Like-radical collection	$1 + \sqrt{2} + \sqrt{2} \to 1 + 2\sqrt{2}$
Radical products	$\sqrt{2}\cdot\sqrt{2} \to 2$, $\sqrt{2}\cdot 3\cdot\sqrt{2} \to 6$
Fraction cancellation	$\frac{3x}{x} \to 3$
Trig identities	$\sin^2 + \cos^2 \to 1$, $\frac{\sin}{\cos} \to \tan$
Exact trig values	$\sin!\left(\frac{\pi}{6}\right) \to \frac{1}{2}$, $\sin!\left(\frac{\pi}{12}\right) \to \frac{\sqrt{6}-\sqrt{2}}{4}$
Symbolic trig	$\sin(2)$ stays symbolic — no closed form exists
Inverse trig values	$\arcsin!\left(\frac{\sqrt{2}}{2}\right) \to \frac{\pi}{4}$
Hyperbolic values	$\sinh(\ln 2) \to \frac{3}{4}$, $\text{arccosh}(3) \to \ln(3+2\sqrt{2})$
Log rules	$\ln(ab) \to \ln a + \ln b$, $\ln(12) \to 2\ln 2 + \ln 3$
Exp/log folding	$\exp(2\ln 3) \to 9$, $\exp(\ln x) \to x$
Partial fractions	Full decomposition via factoring
Common denominator	$\frac{1}{x} + \frac{1}{x+1} \to \frac{2x+1}{x(x+1)}$
Assumption-aware	$\sqrt{x^2} \to x$ when $x > 0$
Repeating decimals	$0.\overline{3} \to \frac{1}{3}$
Factorial & binomial	$n!$, $\binom{n}{k}$ with exact evaluation
GCD / LCM	$\gcd(24, 36) \to 12$

Simplification rewrites are identities in the standard CAS sense — equality in the field of rational functions / at generic points — so $\frac{3x}{x} \to 3$ and $\exp(\ln x) \to x$ without carrying pointwise domain caveats ($x \neq 0$, $x > 0$). Domain-sensitive rewrites that genuinely change answers (like $\sqrt{x^2}$) are gated on declared assumptions instead. The equality notion and its boundaries are documented in docs/result-status.md.

Calculus

Feature	Example
Differentiation (chain rule)	$\frac{d}{dx}\sin(x^2) \to 2x\cos(x^2)$
All 24 trig/hyperbolic functions	sin, cos, ..., arccoth — derivatives and integrals
8 integration methods	polynomial, parts, u-sub, trig, partial fractions, ...
Risch algorithm	proves non-elementarity with certificate
Special function recognition	$\int e^{-x^2} \to \tfrac{\sqrt{\pi}}{2}\mathrm{erf}(x)$, $\int \tfrac{e^x}{x} \to \mathrm{Ei}(x)$, $\int \tfrac{dx}{\ln x} \to \mathrm{li}(x)$ — named alongside the impossibility proof
Multi-extension towers	$\int(!e^x\ln x + \frac{e^x}{x}),dx = e^x\ln x + C$
Parametric integration	$\int\frac{dx}{x^2+a} = \frac{1}{\sqrt{a}}\arctan!\frac{x}{\sqrt{a}} + C$
Exact definite integrals	$\int_0^1\frac{dx}{x^2+1} = \frac{\pi}{4}$
Taylor series	exact rational coefficients, symbolic center
Limits	L'Hôpital, series expansion, one-sided, at infinity

Equation Solving

Feature	Example
Degree 1–4 exact	Cardano, Ferrari
Exact radical roots	$x^2-2=0 \to x = \pm\sqrt{2}$
Parametric	$ax^2+bx+c=0 \to \frac{-b \pm \sqrt{b^2-4ac}}{2a}$
Systems	exact Gaussian elimination, polynomial substitution
Inequalities	$x^2-4 > 0 \to (-\infty,-2) \cup (2,\infty)$
Rational equations	$\frac{1}{x} = 2 \to x = \frac{1}{2}$

Summation & Products

Feature	Example
Faulhaber's formulas	$\sum k^2 = \frac{n(n+1)(2n+1)}{6}$
Geometric series	$\sum r^k = \frac{r^{n+1}-1}{r-1}$
Telescoping	$\sum!\left(\frac{1}{k} - \frac{1}{k+1}\right) = \frac{n}{n+1}$
Product notation	$\prod_{k=1}^{5} k = 120$
Symbolic products	$\prod_{k=1}^{n} c = c^n$

ODEs & Series

Feature	Example
Separable	$\frac{dy}{dx} = g(x)\cdot h(y)$
First-order linear	integrating factor
Second-order constant-coefficient	$ay'' + by' + cy = 0$
Power series solutions	Hermite, Legendre, arbitrary order
Formal power series	lazy eval, composition, Lagrange inversion

Linear Algebra

Feature	Example
Determinant, inverse	exact over $\mathbb{Q}$
Eigenvalues	symbolic ($2\times 2$, $3\times 3$), numerical (up to $4\times 4$)
Systems	$Ax = b$, RREF
Algebraic number fields	exact arithmetic in $\mathbb{Q}(\alpha)$

Verification

Feature	Description
Reasoning-chain verification	verify_chain: per-step relations (equals, derivative_of, integral_of, substitution, implies, solution_of, factored_form_of), per-step verdict + mechanism, chain status = minimum evidence across steps
Numeric cross-check	12 test points, assumption-aware, counterexample on FAIL
Exact refutation	inside the polynomial/rational fragment, disagreements are established in exact rational arithmetic — no floating-point tolerance; x = x + 10^{-15} is refuted, not tolerated
Expression equivalence	simplify-and-compare, then assumption-aware sampling
Non-elementarity proofs	Risch algorithm certificates; recognized special-function antiderivatives (erf, Ei, li) named alongside the certificate, guarded by a differentiation round-trip
Result status	evidence taxonomy on every response — exact / verified / approximate / heuristic / unable_to_compute / provably_impossible
Error propagation	float paths carry a first-order propagated error bound; significant_digits gates what may be claimed, zero digits is a refusal, and cancellation is attributed (rewritable) vs ill-conditioning (not)
Coded caveats	every caveat is {code, message} from a fixed registry; every refusal carries its reason as a code — agents route on codes, never prose
Machine-readable verdicts	pass / fail / inconclusive on verify, equivalent, verify_chain — outcomes are fields, not prose; a bounded comparison that can neither confirm nor refute says inconclusive with the bound published
Self-checking	transcendental simplifications and integration round-trips are independently verified before being blessed

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MCP Server

The arithma-mcp binary speaks MCP over stdio. 17 tools with LaTeX I/O:

Tool	Purpose
format	Parse and normalize LaTeX without simplifying
simplify	Reduce an expression to canonical form
differentiate	Symbolic derivative
integrate	Indefinite/definite; proves non-elementary when applicable, naming the special-function antiderivative (erf, Ei, li) when recognized
substitute	Replace a variable with an expression
solve	Equations or inequalities
solve_system	Systems of linear/polynomial equations
factor	Irreducible factoring over $\mathbb{Q}$
partial_fractions	Decompose $P(x)/Q(x)$
limit	Symbolic limits
taylor_series	Series expansion with exact coefficients
evaluate	Numerical evaluation — exact when possible; float results carry approximate status with propagated error bound and significant-digit count, and refuse rather than return digit-free noise
matrix	Determinant, inverse, eigenvalues, rank, RREF, $Ax=b$
equivalent	Check if two expressions are equal
verify	Numerically cross-check at multiple test points
verify_chain	Verify a multi-step derivation, step by step, with per-step verdicts and evidence
solve_ode	First-order, constant-coeff, and power series

verify_chain takes an ordered list of steps, each declaring its relation to the previous one:

{
  "steps": [
    { "label": "f",  "expr": "x^3 - x" },
    { "label": "factored", "expr": "x(x-1)(x+1)", "relation": "factored_form_of" },
    { "label": "f'", "expr": "3x^2 - 1", "relation": "derivative_of", "variable": "x" }
  ]
}

Each step reports verdict (pass/fail/inconclusive), the mechanism that actually ran (canonical_form_Q, differentiation_roundtrip, …), and its evidence class. A wrong step comes back with the counterexample that refutes it. For incremental use, send a two-step chain of the previous and new step.

All tools accept an optional assumptions parameter:

{
  "expr": "\\sqrt{x^2}",
  "assumptions": {"x": ["positive"]}
}

Valid assumptions: positive, nonnegative, negative, nonzero, real, integer.

Setup

Claude Code — add to .claude/settings.json:

{
  "mcpServers": {
    "arithma": {
      "command": "/path/to/arithma-mcp"
    }
  }
}

Claude Desktop — add to your config file (~/Library/Application Support/Claude/claude_desktop_config.json on macOS):

{
  "mcpServers": {
    "arithma": {
      "command": "/path/to/arithma-mcp"
    }
  }
}

---

Web Calculator

The frontend/ directory contains a browser-based calculator built with React and MathLive. Arithma compiles to WebAssembly and runs entirely client-side — same exact-arithmetic engine, no server, no network calls.

wasm-pack build --target web --out-dir frontend/public/pkg
cd frontend && npm install && npm run dev

Then open http://localhost:5173.

---

Command Line

Interactive REPL or one-shot subcommands. Output is human-readable Unicode when attached to a terminal; pipe the output (or pass --latex) to get raw LaTeX instead.

$ arithma simplify "x^2 + 2x + 1"
x² + 2x + 1

$ arithma diff "x^3 + \sin(x)" x
3x² + cos(x)

$ arithma integrate "3x^2" x
x³ + C

$ arithma solve "x^2 - 2 = 0"
x = √2
x = -√2

$ arithma simplify "\sum_{k=1}^{n} k^2"
n · (n + 1) · (2n + 1)/6

$ arithma solve "x^2 - 4 > 0"
(-∞, -2) ∪ (2, ∞)

$ arithma integrate "\exp(-x^2)" x
[provably impossible] This integral has no formula using elementary
functions (polynomials, exponentials, logarithms, trigonometric). This is a
theorem, not a limitation of the tool. — antiderivative in special
functions: √π/2 · erf(x)

All 13 subcommands: format, simplify, differentiate (diff), integrate, solve, factor, prime-factorize (factorint), partial-fractions (pf), evaluate (eval), limit, taylor, substitute (sub), ode.

The CLI and MCP surfaces differ deliberately: the verification tools (verify, equivalent, verify_chain), matrix, and solve_system are MCP-only — they exist for agents consuming structured results — while prime-factorize is CLI-only. Neither list is a subset of the other.

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Building

Cargo workspace: math engine library (root) + CLI (crates/cli/) + MCP server (crates/mcp/).

cargo build --release --workspace         # all crates
cargo build --release -p arithma-cli      # CLI only
cargo build --release -p arithma-mcp-server # MCP server only
cargo test --workspace                    # run all 1813 tests

---

Design Principles

1. Correct first. Exact arithmetic everywhere. Verified idempotency.
2. Well-chosen algorithms. Berlekamp-Zassenhaus, Cardano, Ferrari, Risch. The algorithm matters more than the implementation speed.
3. No hardcoded answers. The system computes results; it does not look them up.
4. LaTeX is the interface. Agents speak LaTeX. We parse it and produce it.
5. Deterministic. Same input, same output. No randomness.
6. Small footprint. Under 5 MB, zero dependencies, compiles to WASM.

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Contributing

See CONTRIBUTING.md for development conventions, CI discipline, and PR workflow.

License

MIT. See LICENSE.