  Human experts write summaries using different techniques, including
extracting a sentence from the document and rewriting it, or fusing various
information from the document to abstract it. These techniques are flexible and
thus difficult to be imitated by any single method. To address this issue, we
propose an adaptive model, GEMINI, that integrates a rewriter and a generator
to mimic the sentence rewriting and abstracting techniques, respectively.
GEMINI adaptively chooses to rewrite a specific document sentence or generate a
summary sentence from scratch. Experiments demonstrate that our adaptive
approach outperforms the pure abstractive and rewriting baselines on three
benchmark datasets, achieving the best results on WikiHow. Interestingly,
empirical results show that the human summary styles of summary sentences are
consistently predictable given their context. We release our code and model at
\url{https://github.com/baoguangsheng/gemini}.
