Add penalty based search for determining derived variable conversion
Add penalty based search for determining derived variable conversion

Each recursive derivation now adds 1 to the overall cost.
As a result, deriving a variable will now use the conversion that contains the minimal amount of derivation steps.

stcorp/harp,stcorp/harp,stcorp/harp,stcorp/harp,stcorp/harp,stcorp/harp