please don't change the fileformat if not necessary (only necessary to describe new features in LyX 2.1). This helps me a lot keeping all language and release versions in sync and to update all
#LyX 2.1 created this file. For more info see http://www.lyx.org/
#LyX 2.1 created this file. For more info see http://www.lyx.org/
\begin_document
\begin_header
\textclass book
\begin_document
\begin_header
\textclass book
\font_roman default
\font_sans default
\font_typewriter default
\font_roman default
\font_sans default
\font_typewriter default
\font_default_family default
\use_non_tex_fonts false
\font_sc false
\font_default_family default
\use_non_tex_fonts false
\font_sc false
\pdf_quoted_options "linkcolor=black, citecolor=black, urlcolor=blue, filecolor=blue,pdfpagelayout=OneColumn, pdfnewwindow=true, pdfstartview=XYZ, plainpages=false"
\papersize default
\use_geometry false
\pdf_quoted_options "linkcolor=black, citecolor=black, urlcolor=blue, filecolor=blue,pdfpagelayout=OneColumn, pdfnewwindow=true, pdfstartview=XYZ, plainpages=false"
\papersize default
\use_geometry false
-\use_package amsmath 0
-\use_package amssymb 0
-\use_package esint 0
-\use_package mathdots 1
-\use_package mathtools 0
-\use_package mhchem 1
-\use_package undertilde 0
+\use_amsmath 0
+\use_esint 0
+\use_mathdots 1
+\use_mhchem 1
-\cite_engine_type numerical
-\biblio_style plain
\use_bibtopic false
\use_indices false
\paperorientation portrait
\suppress_date false
\use_bibtopic false
\use_indices false
\paperorientation portrait
\suppress_date false
\use_refstyle 0
\index Index
\shortcut idx
\use_refstyle 0
\index Index
\shortcut idx
\align center
\begin_inset Tabular
<lyxtabular version="3" rows="7" columns="2">
\align center
\begin_inset Tabular
<lyxtabular version="3" rows="7" columns="2">
-<features rotate="0" tabularvalignment="middle">
+<features tabularvalignment="middle">
<column alignment="center" valignment="top" width="0pt">
<column alignment="center" valignment="top" width="0pt">
<row>
<column alignment="center" valignment="top" width="0pt">
<column alignment="center" valignment="top" width="0pt">
<row>