diff --git a/bin/pruebas_d4rt.dart b/bin/pruebas_d4rt.dart
index f9da874..90f6e8a 100644
--- a/bin/pruebas_d4rt.dart
+++ b/bin/pruebas_d4rt.dart
@@ -1,4 +1,3 @@
-import 'package:d4rt_formulas/d4rt_formulas.dart' as pruebas_d4rt;
 import 'package:d4rt/d4rt.dart';
 
 void main() {
diff --git a/example/formula_evaluation_example.dart b/example/formula_evaluation_example.dart
index d629036..da1ca41 100644
--- a/example/formula_evaluation_example.dart
+++ b/example/formula_evaluation_example.dart
@@ -4,6 +4,7 @@
 /// 1. Create formulas with input/output specifications
 /// 2. Evaluate formulas with different input values
 /// 3. Handle evaluation errors
+library;
 
 import 'package:d4rt_formulas/d4rt_formulas.dart';
 
diff --git a/lib/ai/FormulaWidget.dart b/lib/ai/FormulaWidget.dart
index 193df1a..9dc8898 100644
--- a/lib/ai/FormulaWidget.dart
+++ b/lib/ai/FormulaWidget.dart
@@ -1,40 +1,7 @@
 import 'package:flutter/material.dart';
 
-class VariableSpec {
-  final String name;
-  final String magnitude;
-  static final MAGNITUDELESS = "magnitudeless";
+import '../formula_models.dart';
 
-  VariableSpec({required this.name, required this.magnitude});
-
-  @override
-  String toString() => 'var($name: $magnitude)';
-
-  @override
-  bool operator ==(Object other) =>
-      identical(this, other) ||
-          other is VariableSpec &&
-              runtimeType == other.runtimeType &&
-              magnitude == other.magnitude &&
-              name == other.name;
-
-  @override
-  int get hashCode => Object.hash(magnitude, name);
-}
-
-class Formula {
-  final String name;
-  final List<VariableSpec> input;
-  final VariableSpec output;
-  final String d4rtCode;
-
-  Formula({
-    required this.name,
-    required this.input,
-    required this.output,
-    required this.d4rtCode,
-  });
-}
 
 class FormulaWidget extends StatelessWidget {
   final Formula formula;
@@ -46,7 +13,7 @@ class FormulaWidget extends StatelessWidget {
   final bool showCode;
 
   const FormulaWidget({
-    Key? key,
+    super.key,
     required this.formula,
     this.fontSize = 16.0,
     this.textColor,
@@ -54,7 +21,7 @@ class FormulaWidget extends StatelessWidget {
     this.padding = const EdgeInsets.all(16.0),
     this.showMagnitudes = true,
     this.showCode = false,
-  }) : super(key: key);
+  });
 
   @override
   Widget build(BuildContext context) {
@@ -99,7 +66,7 @@ class FormulaWidget extends StatelessWidget {
     return Container(
       padding: const EdgeInsets.all(12),
       decoration: BoxDecoration(
-        color: Theme.of(context).colorScheme.surfaceVariant.withOpacity(0.3),
+        color: Theme.of(context).colorScheme.surfaceContainerHighest.withOpacity(0.3),
         borderRadius: BorderRadius.circular(8),
         border: Border.all(
           color: Theme.of(context).dividerColor,
@@ -291,7 +258,7 @@ class FormulaWidget extends StatelessWidget {
           width: double.infinity,
           padding: const EdgeInsets.all(12),
           decoration: BoxDecoration(
-            color: Theme.of(context).colorScheme.surfaceVariant.withOpacity(0.5),
+            color: Theme.of(context).colorScheme.surfaceContainerHighest.withOpacity(0.5),
             borderRadius: BorderRadius.circular(6),
           ),
           child: Text(
diff --git a/lib/d4rt_formulas.dart b/lib/d4rt_formulas.dart
index 96d691f..a98dae2 100644
--- a/lib/d4rt_formulas.dart
+++ b/lib/d4rt_formulas.dart
@@ -2,7 +2,7 @@
 /// 
 /// This library provides data models for representing formulas and an evaluator
 /// for executing them using the d4rt Dart interpreter.
-library d4rt_formulas;
+library;
 
 export 'formula_models.dart';
 export 'formula_evaluator.dart';
diff --git a/lib/formula_models.dart b/lib/formula_models.dart
index a489363..bea9371 100644
--- a/lib/formula_models.dart
+++ b/lib/formula_models.dart
@@ -86,7 +86,7 @@ class Formula {
 
     final formulas = list.map( (set) => Formula.fromSet(set as Map) );
 
-    return formulas.toList(growable: false) as List<Formula>;
+    return formulas.toList(growable: false);
   }
 
   factory Formula.fromSet(Map<Object?, Object?> theSet) {
@@ -119,7 +119,7 @@ class Formula {
     VariableSpec output = parseVar(outputSet);
     String d4rtCode = theSet.get("d4rtCode");
 
-    return new Formula(
+    return Formula(
       name: name,
       input: input,
       output: output,
diff --git a/lib/main.dart b/lib/main.dart
index 7b7f5b6..8fd1cab 100644
--- a/lib/main.dart
+++ b/lib/main.dart
@@ -1,7 +1,30 @@
+import 'package:d4rt_formulas/ai/FormulaWidget.dart';
+import 'package:d4rt_formulas/formula_models.dart';
 import 'package:flutter/material.dart';
 
 void main() {
-  runApp(const MyApp());
+  //runApp(const MyApp());
+  Formula formula = sampleFormula();
+  runApp( MaterialApp( home: FormulaWidget(formula: formula)) );
+}
+
+Formula sampleFormula(){
+  final literal = """
+    {
+      "name": "Newton's second law",
+      "input": [
+        { "name": 'm', "magnitude": 'mass'},
+        { "name": 'a', "magnitude": 'acceleration'}
+      ],
+      "output": { "name": 'F', "magnitude": 'force'},
+      "d4rtCode": '''
+              F = a * m;
+          '''
+    }    
+    """;
+
+  final formula = Formula.fromStringLiteral(literal);
+  return formula;
 }
 
 class MyApp extends StatelessWidget {
diff --git a/pubspec.yaml b/pubspec.yaml
index 00c5a8c..34c42ec 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -37,6 +37,7 @@ dependencies:
   d4rt:
   flutter_d4rt:
 
+  collection: any
 dev_dependencies:
   flutter_test:
     sdk: flutter
diff --git a/test/formula_models_test.dart b/test/formula_models_test.dart
index e572ba7..8e7ac6d 100644
--- a/test/formula_models_test.dart
+++ b/test/formula_models_test.dart
@@ -1,6 +1,4 @@
-import 'dart:convert';
 
-import 'package:d4rt/d4rt.dart';
 import 'package:d4rt_formulas/formula_evaluator.dart';
 import 'package:test/test.dart';
 import 'package:d4rt_formulas/formula_models.dart';
@@ -16,7 +14,7 @@ void main() {
       ],
       "output": { "name": 'F', "magnitude": 'force'},
       "d4rtCode": '''
-              return a * m;
+              F = a * m;
           '''
     };
 
@@ -41,7 +39,7 @@ void main() {
       ],
       "output": { "name": 'F', "magnitude": 'force'},
       "d4rtCode": '''
-              return a * m;
+              F = a * m;
           '''
     }    
     """;