$ARRAY1 = [
            'R: $ARRAY1->[3]',
            'a0',
            'a1',
            'a2',
            'a3',
            'a4',
            'a5',
            'a6',
            'a7',
            'a8',
            'a9'
          ];
$ARRAY1->[0] = \$ARRAY1->[3];