AB + ABC + ABCD + ABCDE + ABCDEF
=(AB +ABC) + (ABCD +ABCDE) + ABCDEF (Commutative Law Law)
=AB + ABCD +ABCDEF (Absorption Law)
=AB +( ABCD +ABCDEF) (Commutative Law Law)
=AB +ABCD (Absorption Law)
=AB
So, simplification of the Boolean expression AB + ABCD + ABCDE + ABCDEF yields AB