         guard
             
             let project:DProject = self.project,
-            var equations:[DEquation] = project.equations?.array as? [DEquation]
+            let equations:[DEquation] = project.equations?.array as? [DEquation]
         
         else
         {

        {
            guard
            
                var polynomials:[DPolynomial] = equation.polynomials?.array as? [DPolynomial],
                let result:DPolynomial = equation.result
            
            else

                        polynomialA:polynomial,
                        polynomialB:result)
                    
                    DManager.sharedInstance?.createManagedObject(
                        entityName:DPolynomial.entityName)
                    { [weak equation] (created) in
                        
                        guard
                        
                            let polynomial:DPolynomial = created as? DPolynomial
                        
                        else
                        {
                            return
                        }
                        
                        equation?.result = polynomial
                    }
                }
            }
            else
            {
                project.removeFromEquations(equation)
                DManager.sharedInstance?.delete(object:equation)
            }
        }
        
