yes, my bad

I tried several solutions without problems. Your code is wrong somewhere.

PowerShell test function is faulty

The term 'in-array' is not recognized as the name of a cmdlet, function, script file, or operable program.
Check the spelling of the name, or if a path was included, verify that the path is correct and try again.

at <ScriptBlock>, /home/codewarrior/test.ps1: line 4
4:     $ans = in-array $a1 $a2