anchor.diff:  this particular generator always returns the same value:*)
   
   (***define-output:ConstantExample***)
  -Gen.constant (1, "Foo") |> Gen.sample 0 10 |> Seq.toList
  +Gen.constant (1, "Foo") |> Gen.sample 0 10
   
   (**In this example, the constant is a complex value (a tuple); it can also be a
   simple value, as for example a string or an integer. Since `Gen.constant`
  
positive.code:  change the result.*)
  
  (***define-output:ElementsExample***)
  Gen.elements [0..9] |> Gen.sample 0 10 |> Seq.toList
  
  (**The result of this expression is a list of ten sample values. Each value is
  a single integer drawn from the collection of numbers from 0 to 9:*)
  
negative.code: distribution is to put more than one identical element into the collection:*)
  
  (***define-output:SkewedElementsExample***)
  Gen.elements ["foo"; "foo"; "bar"] |> Gen.sample 0 10
  
  (**In the above example, the value `"foo"` appears twice, so is twice as likely
  to be drawn from the collection:*)
  