Tree-adjoining grammar (TAG) and combinatory categorial grammar (CCG) are two well-established mildly context-sensitive grammar formalisms that are known to have the same expressive power on strings (i.e., generate the same class of string languages). It is demonstrated that their expressive power on trees also essentially coincides. In fact, CCG without lexicon entries for the empty string and only first-order rules of degree at most 2 are sufficient for its full expressive power.

翻译：树边语法(TAG)和组合语法(组合语法(CCG))是两种久经确立的温和的、对背景敏感的语法形式主义,已知在字符串上具有相同的表达力(即产生相同的字符串语言类型),这表明它们在树上的表达力也基本吻合。事实上,CCG没有空字符串的词汇条目,最多只有一级学位规则2,就足以充分表达力。