Have you TRIED it? Sometimes simply trying a few things out on your own gives you the answer much faster than asking here.
Code:
IF (A=1 AND B<6) OR (A=2) THEN
   LED = 1
ENDIF
Whenever A = 2 LED will turn on.
If A = 1 then B must also be <6 for LED to turn on.

Ugly and verbose but likely smaller:
Code:
IF A = 2 THEN LED = 1
IF (A = 1) AND (B < 6) THEN LED = 1
/Henrik.