Yara rule to find a string near to other strings

yara_example_1.yar

import "math"

rule example {
  meta:
    author = "David Cannings"
    description = "Rule example - finding a chunk of code near other known code"

  strings:
    $chunk = { AA BB CC DD }
    $chunk_prologue = { 11 22 33 44 }
    $chunk_epilogue = { FF EE DD CC }

  condition:
    for 5 i in (1..math.min(#chunk, 50)) : (
      for any j in (1..math.min(#chunk_prologue, 50)) : (
          @chunk[i] > @chunk_prologue[j] and
          @chunk[i] - @chunk_prologue[j] < 20 and
          @chunk[i] - @chunk_prologue[j] > 0 and
      ) 
      and 
      for any k in (1..math.min(#chunk_epilogue, 50)) : (
          @chunk[i] < @chunk_epilogue[k] and
          @chunk_epilogue[k] - @chunk[i] < 20 and
          @chunk_epilogue[k] - @chunk[i] > 0
      )
    )
}