```ruby
require 'spinoza/system/model'
require 'spinoza/system/store'
require 'spinoza/system/table'
require 'spinoza/system/lock-manager'

# A top level entity in the system model, representing one node of
# the distributed system, typically one per host. Nodes are connected by Links.
# Node is stateful.
class Spinoza::Node < Spinoza::Model
  attr_reader :store
  attr_reader :lock_manager
  attr_reader :log, :meta_log
  
  # Outgoing links to peer nodes, as a map `{node => link, ...}`.
  # Use `links[node].send(msg)` to send a message to a peer. Use Node#recv
  # to handle received messages.
  attr_reader :links
  
  # Create a node whose store contains the specified tables and which has
  # its own lock manager.
  def initialize *tables, log: nil, meta_log: nil, **rest
    super **rest
    @store = Spinoza::Store.new *tables
    @lock_manager = Spinoza::LockManager.new
    @links = {}
    @log = log
    @meta_log = meta_log
  end
  
  def link dst, **opts
    links[dst] = Spinoza::Link[timeline: timeline, src: self, dst: dst, **opts]
  end

  def tables
    @tables ||= Set[*store.tables]
  end
  
  class << self
    alias [] new
  end

  def recv msg: raise
    # Defined in subclasses.
  end
end
```

Check for conflicting link definition.
user
```ruby
require 'spinoza/system/model'
require 'spinoza/system/store'
require 'spinoza/system/table'
require 'spinoza/system/lock-manager'

# A top level entity in the system model, representing one node of
# the distributed system, typically one per host. Nodes are connected by Links.
# Node is stateful.
class Spinoza::Node < Spinoza::Model
  attr_reader :store
  attr_reader :lock_manager
  attr_reader :log, :meta_log
  
  # Outgoing links to peer nodes, as a map `{node => link, ...}`.
  # Use `links[node].send(msg)` to send a message to a peer. Use Node#recv
  # to handle received messages.
  attr_reader :links
  
  # Create a node whose store contains the specified tables and which has
  # its own lock manager.
  def initialize *tables, log: nil, meta_log: nil, **rest
    super **rest
    @store = Spinoza::Store.new *tables
    @lock_manager = Spinoza::LockManager.new
    @links = {}
    @log = log
    @meta_log = meta_log
  end
  
  def link dst, **opts
    if links[dst]
      raise "Link from #{self} to #{dst} already exists."
    end
    links[dst] = Spinoza::Link[timeline: timeline, src: self, dst: dst, **opts]
  end

  def tables
    @tables ||= Set[*store.tables]
  end
  
  class << self
    alias [] new
  end

  def recv msg: raise
    # Defined in subclasses.
  end
end
```
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