\documentclass[11pt,a4paper]{article}
\usepackage{preamble}
\begin{document}

\noindent Greek capitals: $\Omega \quad \Sigma \quad \Pi \quad \Lambda \quad \Theta \quad \Phi$\par
\noindent Greek lowercase: $\omega \quad \sigma \quad \pi \quad \lambda \quad \theta \quad \phi \quad \mu$\par

\bigskip
\noindent Variant Greek: $\varepsilon \quad \vartheta \quad \varphi \quad \varpi$\par

\bigskip
\noindent Empty set: $\emptyset$ (should be \texttt{\textbackslash varnothing}: $\varnothing$) \par
\noindent Verify they match: $\emptyset = \varnothing$ ?\par

\bigskip
\noindent Calligraphic: $\mathcal{F} \quad \mathcal{G} \quad \mathcal{P} \quad \mathcal{B} \quad \mathcal{X}$\par
\noindent Blackboard: $\mathbb{R} \quad \mathbb{N} \quad \mathbb{Z} \quad \mathbb{Q} \quad \mathbb{C}$\par
\noindent Math italic: $a, b, c, x, y, z, A, B, C, X, Y, Z$\par

\bigskip
\noindent (For comparison, the Lucida Bright text Ω: \texttt{Ω}; lowercase σ: \texttt{σ})

\end{document}
