[Tex/LaTex] Command \iint already defined

errors

What does the error below mean and how I can fix it? I use www.sharelatex.com. My file main.tex has 100 rows. 

\documentclass[10pt,a6paper]{book}
\usepackage[utf8]{inputenc}
\usepackage[main=slovak,english]{babel}
\usepackage[cm]{fullpage}
\usepackage[a6paper, top=15mm, left=10mm, right=10mm, bottom=10mm,foot=5mm,marginparsep=0mm]{geometry}
%showframe
\usepackage{tipa}
\usepackage{tabularx,booktabs}  %\toprule
\usepackage{listings}
\usepackage{multirow}
\usepackage{longtable}
%\usepackage{lscape}
\usepackage{wasysym} % symbols
\usepackage{amssymb} % symbols
%\usepackage{pdflscape}
%\usepackage{lscape}
\usepackage{hyperref}
\usepackage{marvosym}
\usepackage{framed}
\usepackage{wasysym}
\usepackage{pdflscape}
\usepackage{graphicx}
%\usepackage{amsmath}
\usepackage{color}
\usepackage{tabularx,booktabs}
\usepackage{rotating}
\usepackage{graphicx}
\usepackage{adjustbox}
\usepackage{mathtools}
\usepackage{array,multirow,graphicx}


\newcommand*{\knihaB}{\fontfamily{bch}\selectfont}
\newcommand*{\knihaA}{\fontfamily{phv}\selectfont}
\newcommand*{\knihaC}{\fontfamily{ccr}\selectfont}
\newcommand*{\knihaM}{\fontfamily{cmr}\selectfont}

\newcommand*{\knihaEa}{\fontfamily{qag}\selectfont}
\newcommand*{\knihaEb}{\fontfamily{phv}\selectfont}

\newcommand*{\knihacc}{\fontfamily{pag}\selectfont}
\newcommand*{\knihaaa}{\fontfamily{ccr}\selectfont}
\newcommand*{\knihabb}{\fontfamily{ccr}\selectfont}
%\usepackage{mathtools}
\renewcommand{\thesection}{\arabic{section}}

\begin{document}
\catcode`\-=12
\sloppy

%\clearpage
%\setcounter{secnumdepth}{0} 
%\setcounter{page}{1} 
%\tableofcontents
%\thispagestyle{empty}


{\large

%\input{alphb.txt}
%\input{pronouns.txt}
%\input{tobe.txt}
%\input{havegot.txt}
%\input{can.txt}
%\input{towas.txt}
%\input{could.txt}
%\input{had.txt}
%\input{wouldlike.txt}
%\input{casy.txt}
%\input{inqs.txt}
%\input{should.txt}
%\input{usedto.txt}
%\input{haveto.txt}
%\input{predl1.txt}

%\input{ukaz.txt}
%\input{clen.txt}
%\input{podm.txt}
%\input{ponep.txt}
%\input{mnozs.txt}
%\input{nep_1.txt}
%\input{privlast.txt}
%\input{pridm.txt}
%\input{wh_q.txt}
%\input{nz.txt}
%\input{zast_zam.txt}
%\input{deter.txt}
%\input{spoj.txt}
%\input{numbers.txt}
%\input{adverbs.txt}
%\input{theris.txt}
%\input{slovosled.txt}
%\input{rozkaz.txt}
%\input{week.txt}

}


\end{document}

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Thanks for help.

Best Answer

The wasysym package also defines multiple integral symbols. You can load it with option [nointegrals] if you want to use the amsmath version, or [integrals] if you prefer the wasysym version.

I took the opportunity to clean your preamble: many packages were loaded several times. Also, you don't have to load amsmath if you load mathtools since the latter does it for you.

As your main language has accented letters, you must add \usepackage[T1]{fontenc} to ensure proper hyphenation.

Final comments: it's better to load xcolorthan color, as it can do more things, with option [table] if you intend to use colours in tables, and hyperref should be loaded as the last package, with very few exceptions (most notable cleveref).

\documentclass[10pt,a6paper]{book}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[main=slovak,english]{babel}
\usepackage[cm]{fullpage}
\usepackage[a6paper, top=15mm, left=10mm, right=10mm, bottom=10mm,foot=5mm,marginparsep=0mm]{geometry}
%showframe
\usepackage{tipa}
\usepackage{tabularx,booktabs} %\toprule
\usepackage{listings}
\usepackage{longtable}
\usepackage{amssymb} % symbols
\usepackage[nointegrals]{wasysym} % symbols
%\usepackage{pdflscape}
%\usepackage{lscape}
\usepackage{marvosym}
\usepackage{framed}
\usepackage{pdflscape}
\usepackage[table]{xcolor}
\usepackage{rotating}
\usepackage{adjustbox}
\usepackage{mathtools}
\usepackage{array,multirow,graphicx}
\usepackage{hyperref}    

\newcommand*{\knihaB}{\fontfamily{bch}\selectfont}
\newcommand*{\knihaA}{\fontfamily{phv}\selectfont}
\newcommand*{\knihaC}{\fontfamily{ccr}\selectfont}
\newcommand*{\knihaM}{\fontfamily{cmr}\selectfont}

\newcommand*{\knihaEa}{\fontfamily{qag}\selectfont}
\newcommand*{\knihaEb}{\fontfamily{phv}\selectfont}

\newcommand*{\knihacc}{\fontfamily{pag}\selectfont}
\newcommand*{\knihaaa}{\fontfamily{ccr}\selectfont}
\newcommand*{\knihabb}{\fontfamily{ccr}\selectfont}
%\usepackage{mathtools}
\renewcommand{\thesection}{\arabic{section}}

\begin{document}
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