title: F# Multidimensional Array Types
body: <p>What's the difference between <code>'a[,,]</code> and <code>'a[][][]</code>? They both represent 3-d arrays.
  It makes me write <code>array3d.[x].[y].[z]</code> instead of <code>array3d.[x, y, z]</code>.</p>
  
  <p>Why I can't do the following?</p>
  
  <pre><code>&gt; let array2d : int[,] = Array2D.zeroCreate 10 10;;
  &gt; let array1d = array2d.[0];;
  
  error FS0001: This expression was expected to have type
      'a []    
  but here has type
      int [,]
  </code></pre>