2 

     2 

     3 %\usepackage{amsthm}

     3 %\usepackage{amsthm}

     4 

     4 

     5 \newcommand{\pathtotrunk}{./}

     5 \newcommand{\pathtotrunk}{./}

     6 \input{text/article_preamble}

     6 \input{text/article_preamble}

    43 here to interest the motivated reader.

    43 here to interest the motivated reader.

    44 On the other hand, if you are only going to read this paper once,

    44 On the other hand, if you are only going to read this paper once,

    45 {\bf then don't read this version,} as a more complete version will be available in a couple of months.

    45 {\bf then don't read this version,} as a more complete version will be available in a couple of months.

    46 

    46 

    47 \nn{maybe to do: add appendix on various versions of acyclic models}

    47 \nn{maybe to do: add appendix on various versions of acyclic models}

    49 

    50 

    50 

    51 

    51 

    52 

    52 \input{text/intro}

    53 \input{text/intro}

    53 

    54