# echidna Implementation Plans

> **Historical document** — All planned phases have reached their intended scope.
> This index tracked the initial build-out; no further plan files were created in
> this directory. See the [roadmap](../roadmap.md) for current and future work.

## Plan Index

| # | Plan | Chapters | Status |
|---|------|----------|--------|
| 1 | Core Foundation | 2–3 | Complete |
| 2 | Production Reverse Mode | 4, 7, 12 | Complete |
| 3 | Second-Order Derivatives | 5, 8 | Complete |
| 4 | Sparse Computation | 9, 11 | Complete |
| 5 | Advanced Jacobian Accumulation | 10 | Complete |
| 6 | Higher-Order Derivatives (Taylor Mode) | 13 | Complete |
| 7 | Nonsmooth Extensions | 14 | Complete |
| 8 | Implicit and Iterative Differentiation | 15 | Complete |
