code: public boolean eq(Matrix3D B) {
          Matrix3D A = this;
          if (B.M != A.M || B.N != A.N || B.K != A.K) throw new RuntimeException("Illegal matrix dimensions.");
          for (int i = 0; i < M; i++)
              for (int j = 0; j < N; j++)
              	for (int l = 0; l < K; l++)
              		if (A.data[i][j][l] != B.data[i][j][l]) return false;
          return true;
      }
docs: does A = B exactly?