Renaming on Mac:

  for each in *Eng.gf ;  
  do 
  mv $each $(basename $each Eng.gf)Lat.gf
  done

In-place change:

  sed -e 's/Eng/Lat/g' -i *Lat.gf

Start with the following:

concrete GrammarLat of Grammar = 
  NounLat, 
  VerbLat, 
  AdjectiveLat,
--  AdverbLat,
--  NumeralLat,
  SentenceLat,
--  QuestionLat,
--  RelativeLat,
--  ConjunctionLat,
--  PhraseLat,
  TextX,
  StructuralLat,
--  IdiomLat


