title: pinescript Undeclared identifier error (version2 to version4)
body: <p>I'm considering reverting a code in the library from version 2 to version 3 and then back to version 4 with the pinescript robot tool. but I can't fix the error I got in this part.
  it says it is invalid for version 3.</p>
  <pre><code>line 18: Undeclared identifier `TriggerLineb`;
  line 19: Undeclared identifier `TriggerLineb`;
  line 19: Undeclared identifier `TriggerLinea`
  </code></pre>
  <p>Full code</p>
  <pre><code>//@version=3
  
  study(&quot;breakout and swing&quot;,overlay=true)
  res1 = input(title=&quot;Close Time Frame&quot;, type=resolution, defval=&quot;D&quot;)
  cld=security(tickerid, res1, close[1])
  opd=security(tickerid,res1, open[1])
  hd=security(tickerid, res1, high[1])
  ld=security(tickerid, res1, low[1])
  tu=(cld +opd)/2 
  
  ChanLength=input(40,&quot;high/lowChannel barback&quot;)
  UpperBand = highest( high, ChanLength ) 
  LowerBand = lowest( low, ChanLength ) 
  
  
  LowRef= iff(low &lt;= LowerBand,highest(high,2) ,0)
  HighRef =iff( high &gt;= UpperBand,lowest(low,2),0)
  TriggerLineb = LowRef ==0 and LowRef[1]!=0? max(highest(high,2),LowRef[1]) :HighRef==0 and HighRef[1]!=0?min(lowest(low,2),HighRef[1]):nz(TriggerLineb[1])
  TriggerLinea = LowRef!=0 ? TriggerLineb[1]- 1.272 * ( TriggerLineb[1] - LowerBand[1] ):LowRef==0 and crossover(close,TriggerLineb )?LowerBand[1]+.7886* (  UpperBand[1]- LowerBand[1] ): HighRef!=0 ?1.272 * ( UpperBand[1] - TriggerLineb[1] )+TriggerLineb[1] : HighRef==0 and crossunder(close,TriggerLineb)?UpperBand[1]-.786* ( UpperBand[1] - LowerBand[1] ):nz(TriggerLinea[1])
  
  plot( tu, &quot;Breakout&quot;,color=white ,style=line,linewidth=2,transp=20) 
  </code></pre>