Difference between N-rules and L-rules

N-rules and L-rules are basically the same. The only difference is that L-rules are part of the Transformation Grammar and, therefore, applies after tokenization, whereas N-rules constitute the N-grammar, and apply before tokenization. This means that N-rules may only deal with strings or regular expressions, whereas L-rules may also deal with other elements (such as features and UW's):

• L-rule
  • ("I")(BLK)("am"):=("I'm"); (I am>I'm)
  • ("a",PRE)(BLK)("a",ART):=("à",+ART,+CTC); (a a>à)
  • ("de",PRE)(BLK)("le",ART):=("du",+ART,+CTC); (de le>du)
• N-rule
  • ("I")(" ")("am"):=("I'm"); (replace "I am" by "I'm")

Note, in the above, that we may use dictionary features (such as BLK, PRE, ART) in L-rules, but we cannot use any dictionary feature in N-rules. The only features available in N-rules are the system-defined features, such as SHEAD (beginning of the sentence) and STAIL (end of the sentence).