/usr/share/games/cuyo/rechnen.ld is in cuyo-data 2.0.0brl1-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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#   Copyright 2005,2006,2008 by Mark Weyer
#   Maintenance modifications 2006,2008,2011 by the cuyo developers
#
#   This program is free software; you can redistribute it and/or modify
#   it under the terms of the GNU General Public License as published by
#   the Free Software Foundation; either version 2 of the License, or
#   (at your option) any later version.
#
#   This program is distributed in the hope that it will be useful,
#   but WITHOUT ANY WARRANTY; without even the implied warranty of
#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#   GNU General Public License for more details.
#
#   You should have received a copy of the GNU General Public License
#   along with this program; if not, write to the Free Software
#   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
#
Rechnen = {
  name = "Calculations"
  author = "Mark Weyer"
  pics = zahl*3
  greypic = grau
  startpic = mreGrasgrau.xpm
  startdist = "BBBBBBBBBB"
  chaingrass[hard] = 1
  <<semiglobal.init={falling_speed=4;};>>
  zahl = {
    pics = mreBlack.xpm,mreRed.xpm,mreBlue.xpm
    <<
      var operator,operatorart;
      zahl.init = {
        if 1:3
          -> {operator = 1; operatorart=rnd(2); weight=0;}
          else {weight = rnd(11)};
      };
      zahl = {
        if operator -> {
          if ??1???1? && !operator@(1,0) && !operator@(-1,0) -> {
            operator=0;
            if operatorart==0 # Addition
              -> weight=weight@(1,0)+weight@(-1,0)
              else weight=weight@(1,0)*weight@(-1,0);
            kind@(1,0)=nothing;
            kind@(-1,0)=nothing;
          }
          else if 1???1??? && !operator@(0,1) && !operator@(0,-1) -> {
            operator=0;
            if operatorart==0 # Addition
              -> weight=weight@(0,1)+weight@(0,-1)
              else weight=weight@(0,1)*weight@(0,-1);
            kind@(0,1)=nothing;
            kind@(0,-1)=nothing;
          };
        };
        file=kind-zahl;
        schema4;
        switch {
          operator -> {pos=operatorart+24; *;};
          weight<10 -> {pos=5+2*weight; *;};
                    -> {
                         pos=4+2*((weight/10)%10); qu=Q_TL; *; qu=Q_BL; *;
                         pos=4+2*(weight%10);      qu=Q_TR; *; qu=Q_BR; *;
                       };
        };
      };
    >>
    numexplode = 100
  }
  grau = {
    pics=mreGrasgrau.xpm
    <<
      grau.init={if 1:5 -> kind=nothing;};
      grau={
        if kind@(0,1)==grau
          -> kind=nothing
        else *;
      };
    >>
  }
}
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