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Valuation Functions

• C: Program-session -> File-system -> (Log × File-system)

  Program-session takes a file system and produces a log file and an updated file system.

• S: Command-sequence -> Openfile -> (Log × Openfile)

  Command-sequence takes an open file and produces a log and an updated file.

• C: Command -> Openfile -> (String × Openfile)

  Command takes an open file and produces a log message and an updated file.