DB<102> @data1 = ( "a 1 a", "a 2 T", "a 3 C" );
 => ("a 1 a", "a 2 T", "a 3 C")

  DB<103> @data2 = ( "a 2 Y", "a 3 R", "a 4 Q", "b 5 R" );
 => ("a 2 Y", "a 3 R", "a 4 Q", "b 5 R")

  DB<104> $regex = join "|" , map {/^(\w\s+\d)/} @data1
 => "a 1|a 2|a 3"

  DB<105> grep { /^($regex)/ } @data2
 => ("a 2 Y", "a 3 R")