           delta -= 1
         }
         self.cells[row][column].flatCharIndex
-          = self.oneDimCellIndex(forRow: row, column: column) + delta
+        = self.oneDimCellIndex(forRow: row, column: column) + delta
       }
     }
   }


  func isSane(_ position: Position) -> Bool {
    if position.column < 0
         || position.column >= self.size.width
         || position.row < 0
         || position.row >= self.size.height {
      return false
    }


    var delta = 0
    if rowStart > 0 {
      delta = self.cells[rowStart - 1][self.size.width - 1].flatCharIndex
              - self.oneDimCellIndex(forRow: rowStart - 1,
                                     column: self.size.width - 1)
    }

    for row in rowStart...rowEndInclusive {
