\documentclass{article}

\newcommand{\be}{\begin{enumerate}}
\newcommand{\ee}{\end{enumerate}}

\usepackage{amsmath} % Needed for user-defined functions such as sinc.
\newcommand{\sinc}{\operatorname{sinc}}

\usepackage{amssymb} % Needed to define the symbols of the real numbers, etc.
\newcommand{\field}[1]{\mathbb{#1}} % Needed for the same purpose as above.
\newcommand{\C}{\field{C}}
\newcommand{\R}{\field{R}}
\newcommand{\Z}{\field{Z}}
\newcommand{\Q}{\field{Q}}
\newcommand{\N}{\field{N}}