```ruby
require 'rubygems'
require 'ruby2ruby'

begin
  require 'parse_tree'
  require 'parse_tree_extensions'
rescue LoadError
  require 'ruby_parser'
  require 'sexp_processor'
  require 'file/tail'
end

module Sourcify

  ROOT = File.dirname(File.expand_path(__FILE__))

  class << self
    def require_rb(*args)
      require File.join(ROOT, 'sourcify', *args)
    end
  end

end

Sourcify.require_rb('proc')
```

Enforce ParseTree mode for 1.8.6.
user
```ruby
require 'rubygems'
require 'ruby2ruby'

begin
  require 'parse_tree'
  require 'parse_tree_extensions'
rescue LoadError
  raise if RUBY_VERSION == '1.8.6' # support for code scanner in 1.8.6 is too tedious
  require 'ruby_parser'
  require 'sexp_processor'
  require 'file/tail'
end

module Sourcify

  ROOT = File.dirname(File.expand_path(__FILE__))

  class << self
    def require_rb(*args)
      require File.join(ROOT, 'sourcify', *args)
    end
  end

end

Sourcify.require_rb('proc')
```
assistant