Readme file.

reactor/README.md

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+# Constraints Reactor
+
+An engine for evaluating constraint rules. 
+
+Written in Kotlin and Java.
+
+This is an implementation of the [Constraint Handling Rules](http://www.informatik.uni-ulm.de/pm/fileadmin/pm/home/fruehwirth/constraint-handling-rules-book.html) semantics with custom extensions, influenced by [JCHR](https://dtai.cs.kuleuven.be/CHR/JCHR/). 
+
+The main features are built-in support for **terms** as the data structure, including terms **unification**, and **logical variables**.
+
+The use of terms as constraint parameters enables to implement optimizations for handling multi-head rules. Also, this implementation relies heavily on term unification when matching rules.
+   
+Logical variables enable to pass parameters to constraints as indirect references, which may be assigned later. Assigning a value to an unbound logical variable reactivates the constraint in which it serves as a parameter. Two logical variables may be joined to be treated as one.    
+
+NOTE: this implementation does not include support for parsing the CHR syntax. 
+
+
+## License
+
+Copyright 2014-2017 JetBrains s.r.o.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.