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% A monomial of three variables
$xyz$

% A sum of two numeric constants
$\infty+\pi$

% A multiplication of two numeric literals
$2\frac{3}{4}$

% Incomplete terms / typically broken by alignments:
% but also may appear inside sub/super-scripts
$a+$

% Signed terms
$-xy$

% mixed sum of monomials
\[ ab + cd - ef + gh \]

% polynomial
\[ ab + c^2d^3 - ef^5 + g^{-1}h \]

\end{document}