The 'Exorcised' elite package in The Radical's Handbook and the 'Dark Pact' in the main rulebook allow for halving of Corruption. Armour of Contempt subtracts one from Corruption gained. Which of these should be applied first?

I'm leaning towards applying the halving first - and then the subtract one. That way getting a Dark Pact or Exorcised doesn't detract from the Armour of Contempt talent's utility.

If CP is the number of points gained, you are talking about solving 0.5*CP-1. This is a simple math problem, which is solved using the standard order of operations:

http://en.wikipedia.org/wiki/Order_of_operations#The_standard_order_of_operations

The standard order of operations, or precedence, is expressed in the following chart.

exponents and roots
multiplication and division
addition and subtraction

So do the division first.

Bilateralrope is correct.

Wait, is that how armour of contempt works? We've been treating it like corruption armour with an ap of 1.