In other words, we want to check whether a TAG derivation tree is a valid TT-MCTAG derivation tree without deciding, for every occurrence of some argument β, which of the h(β)-nodes represents its head.
here we have a derivation tree D with root node v, Lab(v) = γ q,r and a derivation tree D ′ with root node v ′ , Lab(v ′ ) = γ q ′ ,r ′ .