#include <iostream>
#include <fstream>
#include <vector>
#include <set>
#include <climits>
#include <string>
using namespace std;

#define alps ('Z'-'A'+1)

void solve(vector<vector<bool> > &ord,vector<bool> &use,int cur,set<int> &found,vector<string> &res)
{
  if (cur==found.size()){
    res.push_back("");
    return;
  }

  for (int i=0;i<alps;i++){
    if (use[i]) continue;
    bool minimum=true;
    for (int j=0;j<alps;j++)
      if (!use[j]&&ord[j][i]) minimum=false;
    if (!minimum)
      continue;

    int n=res.size();
    use[i]=true;
    solve(ord,use,cur+1,found,res);
    use[i]=false;

    for (;n<res.size();n++)
      res[n]=(char)('A'+i)+res[n];
  }
}

int main()
{
  ifstream cin("frame.txt");

  for (int w,h;cin>>h>>w,w!=0||h!=0;){
    vector<vector<int> > bd(h);
    set<int> found;
    for (int y=0;y<h;y++){
      for (int x=0;x<w;x++){
        char c;cin>>c;
        int n;
        if (c=='.') n=-1;
        else n=c-'A';
        bd[y].push_back(n);
        if (n>=0) found.insert(n);
      }
    }

    vector<int> min_x(alps,INT_MAX),max_x(alps,INT_MIN);
    vector<int> min_y(alps,INT_MAX),max_y(alps,INT_MIN);
    for (int y=0;y<h;y++){
      for (int x=0;x<w;x++){
        int n=bd[y][x];
        if (n<0) continue;

        min_x[n]=min(min_x[n],x);
        max_x[n]=max(max_x[n],x);
        min_y[n]=min(min_y[n],y);
        max_y[n]=max(max_y[n],y);
      }
    }

    vector<vector<bool> > ord(alps,vector<bool>(alps,false));
    for (int i=0;i<alps;i++){
      if (found.find(i)==found.end()) continue;

      int x,y;
      y=min_y[i];
      for (x=min_x[i];x<=max_x[i];x++)
        if (bd[y][x]!=i) ord[i][bd[y][x]]=true;
      y=max_y[i];
      for (x=min_x[i];x<=max_x[i];x++)
        if (bd[y][x]!=i) ord[i][bd[y][x]]=true;
      x=min_x[i];
      for (y=min_y[i];y<=max_y[i];y++)
        if (bd[y][x]!=i) ord[i][bd[y][x]]=true;
      x=max_x[i];
      for (y=min_y[i];y<=max_y[i];y++)
        if (bd[y][x]!=i) ord[i][bd[y][x]]=true;
    }

    vector<bool> use(alps,false);
    vector<string> res;
    for (int i=0;i<alps;i++)
      if (found.count(i)==0)
        use[i]=true;
    solve(ord,use,0,found,res);
    sort(res.begin(),res.end());
    for (int i=0;i<res.size();i++)
      cout<<res[i]<<endl;
    cout<<endl;
  }
  
  return 0;
}