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subsection \<open>Policy Core\<close>
theory 
  PolicyCore
  imports 
     NetworkCore 
     UPF.UPF
begin


text\<open>A policy is seen as a partial mapping from packet to packet out.\<close>

type_synonym ('\<alpha>, '\<beta>) FWPolicy = "('\<alpha>, '\<beta>) packet \<mapsto> unit" 

text\<open>
  When combining several rules, the firewall is supposed to apply the
  first matching one. In our setting this means the first rule which
  maps the packet in question to \<open>Some (packet out)\<close>. This is
  exactly what happens when using the map-add operator (\<open>rule1
  ++ rule2\<close>). The only difference is that the rules must be given in
  reverse order. 
\<close>



text\<open>
  The constant \<open>p_accept\<close> is \<open>True\<close> iff the policy
  accepts the packet. 
\<close>

definition
  p_accept :: "('\<alpha>, '\<beta>) packet \<Rightarrow> ('\<alpha>, '\<beta>) FWPolicy \<Rightarrow> bool" where
  "p_accept p pol =  (pol p = \<lfloor>allow ()\<rfloor>)"

end