lower_triangle.nf

/*typo replace {into ; not ","}*/
Channel
  .from( [[1, "ind"], [2, "may"], [3, "nig"], [4, "pue"], [5, "uni"], [6, "gem"]] )
  .into{ bel_spec1_ch; bel_spec2_ch }

Channel.from("test1", "test2" ).collect().set{vcf_loc_pair1}

bel_pairs_ch = Channel
  .from( "test1" )
  .join( vcf_loc_pair1 )
  .combine(bel_spec1_ch)
  .combine(bel_spec2_ch)
  .filter{ it[2] < it[4] }
  .map{ it[0,1,3,5]}

bel_pairs_ch
  .subscribe { println it }