#include <bits/stdc++.h>   using namespace std;   char c;   int n, m, cnt, f[3600][3];   bool a[60][60], flag, heng[51][51][51], shu[51][51][51];   bool go(int x1, int y1, int x2, int y2) {     if (heng[x1][min(y1, y2)][max(y1, y2)] && shu[y2][min(x1, x2)][max(x1, x2)])       return true;     if (heng[x2][min(y1, y2)][max(y1, y2)] && shu[y1][min(x1, x2)][max(x1, x2)])       return true;     return false;   }   int main() {     cin >> n >> m;     for (int i = 1; i <= n; i++)       for (int j = 1; j <= m; j++) {         cin >> c;         if (c ==  B ) a[i][j] = 1, f[++cnt][1] = i, f[cnt][2] = j;       }     for (int i = 1; i <= n; i++)       for (int j = 1; j <= m; j++)         if (a[i][j]) {           heng[i][j][j] = true;           for (int k = j + 1; k <= m; k++) {             if (a[i][k])               heng[i][j][k] = true;             else               break;           }         }     for (int i = 1; i <= m; i++)       for (int j = 1; j <= n; j++)         if (a[j][i]) {           shu[i][j][j] = true;           for (int k = j + 1; k <= n; k++) {             if (a[k][i])               shu[i][j][k] = true;             else               break;           }         }     flag = true;     for (int i = 1; i < cnt; i++)       for (int j = i + 1; j <= cnt; j++)         if (!go(f[i][1], f[i][2], f[j][1], f[j][2])) {           flag = false;           break;         }     if (flag)       cout <<  YES  << endl;     else       cout <<  NO  << endl;     return 0;   }   