content: import React from 'react'
  import PropTypes from 'prop-types'
  
  import { push } from 'react-router-redux'
  
  const Nav = ({push}) => (
      <div>
          <button onClick={()=>push('./additon')}>加法</button>
          <button onClick={()=>push('./subtraction')}>减法</button>
      </div>
  
  )
  
  export default Nav