Lexical chains of words refer to words that occurred through a discourse and that is related in the same category, or linked categories. They showed that the number and density of chain correlated with the topic structure.

Hamilton College

Discourses cohere by talking about the same topics and subtopics, and drawing on the same semantic fields in doing so.

Local Coherence

An on-going but a helpful book resource about NLP
https://web.stanford.edu/~jurafsky/slp3/

Speech and Language Processing (3rd ed. draft) 

Lexical cohesion refers to the sharing of identical or semantically related words in nearby sentences.

Lexical Cohesion

Lexical Chains

The TextTilling algorithm computed the cosine between neighboring text spans (the normalized dot product of vectors of raw word counts), showing that sentences or paragraph in a subtopic have high cosine with each other, but not with sentences in a neighboring subtopic.

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