README.md in y_nelson-2.0.1 vs README.md in y_nelson-2.0.3

@@ -1,25 +1,32 @@
 # YNelson
 
-TODO: Write a gem description
+`YNelson` is a domain model and a simulator of _Nelson_ _nets_. A _Nelson_ _net_
+is a Petri net, whose elements (places and transitions) have at the same time
+the aspect of cells of the Zz structures described by Ted Nelson.
 
-## Installation
+## Petri net aspect
 
-Add this line to your application's Gemfile:
+`YNelson` provides a _domain_ _specific_ _language_ (DSL), that can be loaded by:
+```ruby
+  require 'y_nelson'
+  include YNelson
+```
+`YNelson` DSL includes aspects of `YPetri`. It means, that it has the same
+abilities as `YPetri`. See `YPetri` gem
+[for Petri net aspect usage examples](https://github.com/boris-s/y_petri).
 
-    gem 'y_nelson'
+## Zz structure aspect
 
-And then execute:
-
-    $ bundle
-
-Or install it yourself as:
-
-    $ gem install y_nelson
-
-## Usage
-
-TODO: Write usage instructions here
+`YNelson` places and transtitions are both objects (or "cells", using Ted
+Nelson's terminology) of a Zz structure. They exist in a multidimensional space,
+where they can have at most 2 sides -- _posward_ and _negward_ -- in each
+dimension. Zz structure aspect in general is defined in
+[yzz gem](https://github.com/boris-s/y_petri). In addition to this, `YNelson`
+automatically creates Zz connections in parallel to arcs of a Petri net. This
+way, places and transtions of a Petri net, whose relations are normally captured
+by arcs, can also have other relations defined, captured by Zz dimensions. Zz
+structure aspect is still in alpha stage at present.
 
 ## Contributing
 
 1. Fork it
 2. Create your feature branch (`git checkout -b my-new-feature`)