Theory PolicyCore

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subsection ‹Policy Core›
theory 
  PolicyCore
  imports 
     NetworkCore 
     UPF.UPF
begin


text‹A policy is seen as a partial mapping from packet to packet out.›

type_synonym (, ) FWPolicy = "(, ) packet  unit" 

text‹
  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 Some (packet out)›. This is
  exactly what happens when using the map-add operator (rule1
  ++ rule2›). The only difference is that the rules must be given in
  reverse order. 
›



text‹
  The constant p_accept› is True› iff the policy
  accepts the packet. 
›

definition
  p_accept :: "(, ) packet  (, ) FWPolicy  bool" where
  "p_accept p pol =  (pol p = allow ())"

end