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README.md

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+# Deriv
+
+Deriv is a basic, command-line symbolic differentiation engine,
+supporting reasonably standard mathematical notation for input and
+output.
+
+An example interaction:
+
+```
+> 2x^2 + 3x
+4x + 3
+> x^3 - x^2
+3x^2 + -2x
+```
+
+See [LOG.md](LOG.md) for a log of the development process.
+
+## Building and Running
+
+Deriv is written in Rust and uses Cargo as its build system.  The Rust
+toolchain (including Cargo) is most easily installed with
+[Rustup](https://rustup.rs/).
+
+Given that you have a toolchain installed, the REPL can be ran with:
+
+```
+cargo run --bin repl
+```
+
+Alternatively, to only build the project:
+
+```
+cargo build
+```
+
+To run the test suite:
+
+```
+cargo test
+```
+
+## Limitations
+
+Deriv currently has several limitations:
+
+- Only the variable "x" is currently supported.
+- Exponents must be constant (so e.g. "x^x" is unsupported)
+- Expression simplification is quite limited, many output expressions
+  may not be fully simplified
+- There are no built-in constants like e or π
+- Functions such as sine, cosine and natural logarithms are not
+  supported
+- The input must be UTF-8 Basic Latin / ASCII-compatible text
+
+## License
+
+Deriv is Copyright © Camden Dixie O'Brien, and is available under the
+Komorebi 2.0.0 license.  See [LICENSE.md](LICENSE.md) for details.