- | Get all variables never outputed
getSecretChannels :: AnProcess ProcessAnnotation -> S.Set LVar -> S.Set LVar
getSecretChannels (ProcessAction (New v) _ p) candidates =
  let c = S.insert v candidates in
    getSecretChannels p c

getSecretChannels :: AnProcess ProcessAnnotation -> S.Set LVar -> S.Set LVar
getSecretChannels (ProcessAction (New v) _ p) candidates =
  let c = S.insert v candidates in
    getSecretChannels p c
getSecretChannels (ProcessAction (New v) _ p) candidates =
  let c = S.insert v candidates in
    getSecretChannels p c