Paper/Paper.thy
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  1392   easily construct a universal Turing machine via a universal 
  1392   easily construct a universal Turing machine via a universal 
  1393   function. This is different from Norrish \cite{Norrish11} who gives a universal 
  1393   function. This is different from Norrish \cite{Norrish11} who gives a universal 
  1394   function for Church numbers, and also from Asperti and Ricciotti 
  1394   function for Church numbers, and also from Asperti and Ricciotti 
  1395   \cite{AspertiRicciotti12} who construct a universal Turing machine
  1395   \cite{AspertiRicciotti12} who construct a universal Turing machine
  1396   directly, but for simulating Turing machines with a more restricted alphabet.
  1396   directly, but for simulating Turing machines with a more restricted alphabet.
  1397   \emph{Recursive functions} are defined as the datatype
  1397   Unlike Norrish \cite{Norrish11}, we need to represent recursive functions
       
  1398   ``deeply'' because we want to translate them to abacus programs.
       
  1399   Thus \emph{recursive functions} are defined as the datatype
  1398 
  1400 
  1399   \begin{center}
  1401   \begin{center}
  1400   \begin{tabular}{c@ {\hspace{4mm}}c}
  1402   \begin{tabular}{c@ {\hspace{4mm}}c}
  1401   \begin{tabular}{rcl@ {\hspace{4mm}}l}
  1403   \begin{tabular}{rcl@ {\hspace{4mm}}l}
  1402   @{term r} & @{text "::="} & @{term z} & (zero-function)\\
  1404   @{term r} & @{text "::="} & @{term z} & (zero-function)\\