title: how to modify existing pine-script code from @version2 to @version4?
body: <p>how to resolve the Undeclared identifier 'i1' error in pine script.</p>
  <pre><code>source=close
  c2 = 0.74
  
  i1 = c1*source + c2*nz(i1[1])
  
  </code></pre>