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README.md

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+# mcalc
+mcalc is a calculator for modular arithmetic.
+
+## Quirks
+### Why can't exponents be expressions? Why do they have to be integers?
+This is easiest to explain with an example: what should `2^(3+4)` evaluate to
+modulo 7? In my opinion, it should be 2, since `2^7 = 2 (mod 7)`. However,
+because all the operators in the calculator are implemented as modular
+operators, it will first evaluate `(3+4)` as 0, leading to `2^0 = 1 (mod 7)`. I
+saw three options:
+
+1. Leave this behavior in, even if it's not what I think most people would expect.
+2. Complicate the code by handling exponent expressions non-modularly.
+3. Simply don't let exponents be expressions.
+
+I chose 3.
+
+### Why can't I compute square roots for a composite modulus?
+It is certainly possible to compute modular square roots with a composite
+modulus, and I would like to add the capability at some point, but as
+implemented, the calculator only supports a prime modulus.
+
+### Why is the `ord()` function so slow when the modulus is large?
+Partly because computing [multiplicative
+order](https://en.wikipedia.org/wiki/Multiplicative_order) is a hard problem,
+and partly because I'm too lazy at the moment to implement a slightly more
+efficient algorithm.