c2n2(m):={
  local s,ln_,l,n;
  s:=size(m);
  if (irem(s,2)==1){
  m:=append(m,"F");
  s:=s+1;
  }
  ln_:=[];
  l:=asc(m);
  for (k:=0;k<s;k:=k+2){
  n:=l[k]*26+l[k+1];
  ln_:=append(ln_,n);
  }
  return(ln_);
  };
  n2c2(l):={
  local s,n,m;
  s:=size(l);
  m:="";
  for (k:=0;k<s;k++){
  n:=l[k];
  m:=append(m,char(iquo(n,26)+65));
  m:=append(m,char(irem(n,26)+65));
  }
  return(m);
  };
  affin2(a,b,l):={
  local s;
  s:=size(l);
  for (k:=0;k<s;k++){
  l[k]:=irem(a*l[k]+b,676);
  }
  return(l);
  };
  cesar2(a,b,m):={
  return(n2c2(affin2(a,b,c2n2(m))));
  };