title: How to exclude the second end from an enumerator
body: <p>I need an <code>Enumerator</code> that iterates over <code>n</code> digits from <code>a</code> to <code>b - (b - a) / n.to_f()</code>. I need a left-closed right-open interval with step <code>(b - a) / n.to_f()</code>. How can I get it?</p>
  
  <p>I use <code>a.step(b, (b - a) / n.to_f())</code>, but <code>step</code> returns an <code>Enumerator</code> that iterates over <code>n + 1</code> digits including both ends <code>a</code> and <code>b</code>.</p>