Extend Wren to include a definite iteration command of the form ie1 : iexp ie2 : iexp c : cmd / for id := ie1 to ie2 do c end : cmd idId whose informal semantics agrees with the for command in Pascal. Add inference rules to the structural operational semantics of Wren to give a formal semantics for this new command. may use either Natural Semantics or Structural Operational Semantics..