My question is similar to Is verbatim copying several paragraphs of text with citation considered plagiarism?, but I want to ask about very short, concise wordings. As an example, I read a paper in which the author uses the following sentence:
While in the above description we have specified a local algorithm as a function that maps local neighbourhoods to local outputs, we could equally well […]
Now, instead of copying the exact sentence with its grammatical structure, I want to point the reader to this paper and briefly mention one of the conclusions made in this paper. Consider the sentence
author et al. [citation] show that a local algorithm is a function that maps local neighborhoods to local outputs.
The wording "function that maps local neighborhoods to local outputs" is a verbatim copy from the original source. Of course, I could replace this wording with something else that expresses the same, but I find the original citation very concise and I could not come up with a completely different and equally concise sentence.
I always use quotes in addition to a citation to tell the reader that not only the conveyed ideas and concepts, but also the wording, is not my own intellectual achievement. But in this case, one might argue that a person that has understood the ideas described in the original paper might come up with the exact same wording, hence the wording is not a result of the original author's linguistic style, but rather a direct conclusion of the idea he wants to explain.
Is it acceptable to use this wording with a citation and no quotations, or should you always use quotes for verbatim-copies?