documentclass[letterpaper,12pt,titlepage,oneside,final]{book}

newcommand{package}[1]{textbf{#1}} % package names in bold text
newcommand{cmmd}[1]{textbackslashtexttt{#1}} % command name in tt font
newcommand{href}[1]{#1} % does nothing, but defines the command so the
    % print-optimized version will ignore href tags (redefined by hyperref pkg).
%newcommand{texorpdfstring}[2]{#1} % does nothing, but defines the command
% Anything defined here may be redefined by packages added below...

% This package allows if-then-else control structures.
usepackage{refcheck}
usepackage{ifthen}
newboolean{PrintVersion}
setboolean{PrintVersion}{false}
% CHANGE THIS VALUE TO "true" as necessary, to improve printed results for hard copies
% by overriding some options of the hyperref package below.

%usepackage{nomencl} % For a nomenclature (optional; available from ctan.org)
usepackage{amsmath,amssymb,amstext} % Lots of math symbols and environments
usepackage[pdftex]{graphicx} % For including graphics N.B. pdftex graphics driver

usepackage[pdftex,letterpaper=true,pagebackref=false]{hyperref} % with basic options
        % N.B. pagebackref=true provides links back from the References to the body text. This can cause trouble for printing.
ifthenelse{boolean{PrintVersion}}{   % for improved print quality, change some hyperref options
hypersetup{    % override some previously defined hyperref options
%    colorlinks,%
    citecolor=black,%
    filecolor=black,%
    linkcolor=black,%
    urlcolor=black}
}{} % end of ifthenelse (no else)

setlength{marginparwidth}{0pt}
setlength{marginparsep}{0pt} % width of space between body text and margin notes
setlength{evensidemargin}{0.125in} % Adds 1/8 in. to binding side of all
setlength{textwidth}{6.375in} % assuming US letter paper (8.5 in. x 11 in.) and
% side margins as above
raggedbottom

% The following statement specifies the amount of space between
% paragraphs. Other reasonable specifications are bigskipamount and smallskipamount.
setlength{parskip}{medskipamount}

% The following statement controls the line spacing.  The default
% spacing corresponds to good typographic conventions and only slight
% changes (e.g., perhaps "1.2"), if any, should be made.
renewcommand{baselinestretch}{1} % this is the default line space setting
letorigdoublepagecleardoublepage
newcommand{clearemptydoublepage}{%
  clearpage{pagestyle{empty}origdoublepage}}
letcleardoublepageclearemptydoublepage



newcommand{red}[1]{textcolor{red}{#1}}
%newenvironment{noteH}{begin{quote}smallsf H $clubsuit$~}{end{quote}}

%newenvironment{noteS}{begin{quote}smallsf S $diamondsuit$~}{end{quote}}



begin{document}

%
 begin{equation}
 z_i leq sum_{j in P(i)}  x_j  + sum_{ j in N(i) }  (1-x_j) end{equation}

end{document}