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Comments

 noun :+ [ PROPER_PRONOUN_COMMON ppc ].

May I suggest NTYPE as a shorter feature name?

 def-proper-pronoun-rule := const-ltow-rule &
  [ SYNSEM.LOCAL.CONT.HOOK.INDEX.DEF + ,
    SYNSEM.LOCAL.CAT.HEAD.PROPER_PRONOUN_COMMON proper_pronoun,
    DTR.SYNSEM.LOCAL.CAT.HEAD noun].

It's generally more readable to share paths where you
can:

def-proper-pronoun-rule := const-ltow-rule &
 [ SYNSEM.LOCAL [ CONT.HOOK.INDEX.DEF + ,
                  CAT.HEAD.PROPER_PRONOUN_COMMON proper_pronoun ],
   DTR.SYNSEM.LOCAL.CAT.HEAD noun].