title: How to validate that a field must be true if another field is false
body: <p>Below is a snippet of my validation currently:</p>
  <pre><code>'independent_financial_advisor' =&gt; 'required|boolean',
  'understand_objective' =&gt; 'required|boolean',
  'confirm_objective' =&gt; 'required|boolean',
  'understand_term_held' =&gt; 'required|boolean',
  'tax_relief' =&gt; 'required|boolean',
  </code></pre>
  <p>I need to validate that when <code>independent_financial_advisor</code> is false, the remaining 4 fields below must be true. I could not find any Laravel rule which could do this so I thought about using a closure to create a custom rule.</p>
  <p>The issue with this is that I don't know how to reference another field in a closure to check its value.</p>
  <p>What is the best way to go about this? Thanks</p>