code: function(sbm) {
      // if the matrix ain't square, symmetry is off
      if (sbm.x !== sbm.y) {
        return false
      }
  
      // symmetry status
      var symmetry = true
      // iterate
      for (var i = 0; i < sbm.x; i++) {
        for (var j = 0; j <= i; j++) {
          symmetry = symmetry && ((_.includes(sbm.data[i], j) ^ _.includes(sbm.data[j], i)) === 0)
        }
      }
      // return
      return symmetry
    }
docs: returns true if the matrix is symmetric