     func solveFor(_ symbol: Symbol) {
         let coeff = -1.0 / cells[symbol]!
         cells[symbol] = nil
-        _constant *= coeff
+        constant *= coeff
 
         var newCells = OrderedDictionary<Symbol, Double>()
 

     Reverse the sign of the constant and all cells in the row.
     */
    func reverseSign() {
        _constant = -_constant

        var newCells = OrderedDictionary<Symbol, Double>()


            newCells[symbol] = value
        }

        cells = newCells
    }

    /**
