The infantry or cavalry unit determines the number of battle dice
it will roll in the melee combat including any terrain reductions.
The artillery unit determines the number of battle dice it will roll
including any terrain reductions. The artillery’s battle dice are
added to the battle dice of the friendly unit making the melee
attack. All the dice are rolled together at the same time. There
may be an occasion where the infantry or cavalry unit battle dice
result is Zero. The artillery unit engaging in combined arms will
still roll its determined number of battle dice.
In a Combined Arms Combat, even though the
If you read the rules correct (bold):
The Initial attacker (INF or CAV) determine all his battle dice complete separat, including terrain reduction. If a unit have any "minus" result, this unit have simple 0 dice, no "minus" dice are offset against to other units "plus" dice.
the supporting dice of ART, determine also each battle dice for each single ART, complete separate,
thats the number of battle dice.
Indifferent of the These numbers, the ART only hits with XSW, if the Initial attacker would also hit with XSW, indifferent, if the Initial attacker have 0 or -2 or -4 dice
So the correct battle dice in your example =
LT has 1d (1 block) -2d for Town terrain = -1d = 0 dice
Art (2 hex range) has 3d -1 Town = 2d.
complete = 2 dice and because the LT would General hit with XSW, the ART hits with his 2 dice also with XSW.