DB<125> $a=["A"]
 => ["A"]
 
  DB<126> $b=["B"]
 => ["B"]
 
  DB<127> @a=($a,"$a",$b,"$b")
 => (["A"], "ARRAY(0x96cb0f0)", ["B"], "ARRAY(0x96cfd80)")
 
  DB<128> @b= uniq @a
 => (["A"], ["B"])