text: import React from 'react';
  import { createStackNavigator } from 'react-navigation-stack';
  import MTestScreen from '../screens/MTestScreen';
  import MWorksheetScreen from '../screens/MathsScreens/MWorksheetScreen';
  import MLearnScreen from '../screens/MathsScreens/MLearnScreen';
  
  export const AppStackNavigatorMath = createStackNavigator({
    MTestScreen : {
      screen : MTestScreen,
      navigationOptions:{
        headerShown : false
      }
    },
    MWorksheetScreen : {
      screen : MWorksheetScreen,
      navigationOptions:{
        headerShown : false
      }
    },
    MLearnScreen :{
      screen : MLearnScreen,
      navigationOptions:{
        headerShown : false
      }
    }
  },
    {
      initialRouteName: 'MTestScreen'
    }
  );
  