title: Flexible horizontal constraints between UIImageViews
body: <p>I have to layout 4 image views equi-distant from each other in one row as in the screen shot below. The widths and heights of the image views are proportional to the width and height of the parent view.</p>
  
  <p><img src="https://i.stack.imgur.com/xo1zT.png" alt="flexible horizontal spacing"> </p>
  
  <p>I have tried loads of combinations on the constraints but can never get them to be equi-distant. What is the best way to tackle this?</p>