When is higher level tech is acquired (via trade, gift, invasion etc). The research cost of related undiscovered lower tech should be reduced to reflect the fact of somekind of "reverse engineering" is involved.
The discount can be related to the different in tech level
e.g. level 3 tech gives 10% discount to undiscovered level 2 tech, and 20% to undiscovered level 1 tech. The effect can be cummulative. e.g both level 3 and level 2 tech when acquired, give 30% discount to level 1 tech. (20% from level 3, 10% from level 2)
