Define output variable for multiple outputs of a process to use in the next process

[zillurbmb51]

nextflow.txt
Hi,
I was trying to develop a pipeline from scratch using plink on nextflow. In this I have multiple input in each process and multiple outputs. How could I exactly define output variables (t2 in the script) which can be used in the next process? I was trying as below and getting attached message and output (nextflow.txt). Any help? Also is there any any tutorial/training of using plink in nextflow? I tried to follow https://seqera.io/training/#_multiple_output_files but it does not describe multiple outputs which can be used in the next process.

params.dir='data/'
params.publish="output/"
Channel
.fromFilePairs("${params.dir}*.{bed,bim,fam}",size:3){file -> file.baseName}
.set {data}

process test1 {
publishDir params.publish
input:
set t1, file(bed), file(bim), file(fam) from data
output:
set file("${t2}.bed"), file("${t2}.bim"), file("${t2}.fam") into test1_results
script:
"""
module load plink
plink --bfile ${t1} --maf 0.05 --make-bed --out t2
"""
}
process test2 {
publishDir params.publish
input:
set t2, file(bed), file(bim), file(fam) from test1_results.collect()
output:
set file("${t3}.bed"), file("${t3}.bim"), file("${t3}.fam") into test2_results
script:
"""
plink --bfile ${t2} --maf 0.01 --make-bed --out t3
"""
}