Initial commit

This provides an abstract syntax tree for first-order logic with integer
arithmetics. Initially, the following types of formulas are supported:

- Booleans values (true and false)
- predicates
- negated formulas
- comparisons of terms (<, ≤, >, ≥, =, ≠)
- implications and biconditionals
- conjunctions and disjunctions of formulas
- existentially and universally quantified formulas

In addition, these types of terms are provided:

- Boolean values (true and false)
- integers
- strings
- special integers (infimum and supremum)
- symbolic functions
- variables
- binary operations (addition, subtraction, multiplication, division,
  modulo, exponentiation)
- unary operations (absolute value, numeric negation)

README.md

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+# foliage [![GitHub release](https://img.shields.io/github/release/potassco/foliage.svg?maxAge=3600)](https://github.com/potassco/foliage/releases) [![crates.io](https://img.shields.io/crates/v/foliage.svg?maxAge=3600)](https://crates.io/crates/foliage)
+
+> First-order logic with integer arithmetics in Rust
+
+This Rust crate provides an abstract syntax tree for first-order formulas with integer arithmetics.
+
+## Supported Formulas
+
+- Booleans values (`true` and `false`)
+- predicates
+- negated formulas
+- comparisons of terms (<, ≤, >, ≥, =, ≠)
+- implications and biconditionals
+- conjunctions and disjunctions of formulas
+- existentially and universally quantified formulas
+
+## Supported Terms
+
+- Boolean values (`true` and `false`)
+- integers
+- strings
+- special integers (infimum and supremum)
+- symbolic functions
+- variables
+- binary operations (addition, subtraction, multiplication, division, modulo, exponentiation)
+- unary operations (absolute value, numeric negation)