Declaretheorem

Declaretheorem is a command in the LaTeX typesetting system, specifically within the amsthm package, used to define new theorem-like environments. These environments are commonly used in mathematical and scientific documents to typeset statements such as theorems, definitions, lemmas, corollaries, and propositions in a standardized and visually distinct manner.

When a new theorem environment is declared using declaretheorem, LaTeX automatically handles the numbering of these statements. This numbering is typically sequential within the document, and can be reset by chapter or section depending on the configuration. The amsthm package provides several predefined styles for theorem environments, such as "plain" (which typically uses italics for the theorem text), "definition" (which usually uses upright text), and "remark" (which also uses upright text). Users can also define custom styles.

The basic syntax for declaretheorem is \declaretheorem[options]{environment name}. For example, \declaretheorem{theorem} would create a new environment named "theorem". This environment can then be used within the document using \begin{theorem} ... \end{theorem}. The options can specify the numbering style, the heading font, and the separation between environments. This command is crucial for maintaining consistency and readability in formal academic writing.