Blocking with protection, and trample

[Randon Ashcroft]

I am at a loss at finding a proper ruling so it shouldn't hurt to ask the community ^^ a friend and I played a bit of magic and came to an impasse, he attacked with 4/2 with trample and I blocked issuing my cartel aristocrat after using the gain protection ability from a color of the attacker. Problem is does any damage go through? We think it does but it would be nice to have hard evidence to it you know?

[Wally]

Yes! Trample is the key here.
{Cartel Aristocrat} is a 2/2

Trample gives the creature the ability to assign any unassigned damage to the player, AFTER assigning enough to kill the creature.

Therefore, the 4/2 assigns the aristocrat 2 damage and is left with 2 to deal on to the player.

Both creatures would normally die, except the aristocrat is given prevention from the damage, and the damage is then reduced to 0.

{Cartel Aristocrat} survives, 4/2 creature dies.

For the rulings on trample see 702.18
For the rulings on protection see 702.15