Lexicalized Tree-Adjoining Grammars (LTAG) - ad-teaching.infor...

Adjunction Constraints
Given TAG G = (N, T , I , A, S)
We specify for each node n of a tree in I ∪ A:
OA ∈ {⊥, ⊤} : obligatory adjunction
Boolean specifying whether adjunction at n is mandatory
SA ⊆ A : selective adjunction
Set of auxiliary trees authorized for adjunction at n
Also often used:
NA ∈ {⊥, ⊤} : null adjunction
Shorthand for the special case OA = ⊥ ∧ SA = ∅
Remarks
• OA = ⊤ ∧ SA = ∅ is not allowed.
• β ∈ SA(n) only if root label of β equal to label of n.
• Substitution nodes must have NA = ⊤.
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