title: R code to test the difference between coefficients of regressors from one regression
body: <p>I want to test whether coefficients in one linear regression are different from each other or whether at least one of them is significantly different from one certain value, say 0, this seems quite intuitive to do in Stata. For example</p>
  
  <p><code>webuse iris
  reg iris seplen sepwid petlen
  seplen==sepwid==petlen
  seplen==sepwid==petlen==0
  </code></p>
  
  <p>I wonder how I can do this if I want to test this in R?</p>