I am trying to call two diff files types in a loop.

I have a1.in-a10.in files and b1.out-b10.out files. 
I wanna access both files simultaneously. I dont want to use nested loops but simultaneously.

```
for f1,f2 `ls *.in` `ls *.out`;do
echo "$f1 $f2"
done

```

I get f1 and f2 not valid identified error