Zodiac Compatibility
The classical relationship between two animals — as a branch relationship, stated as what the system says, without a verdict attached.
This returns the classical relationship between the two earthly branches. It is one input among several — the year animal is the coarsest of the four pillars, and the classical sources never read a match from the year alone.
What the system actually compares
The twelve animals are the twelve earthly branches. The classical relationships between them are fixed and few: the six pairings (六合), the four three-fold groups (三合), the six oppositions (六冲) and the six harms (六害). Anything beyond those belongs to popular practice rather than to the system.
The year animal is also the coarsest of the four pillars. The classical sources never read a match from the year alone — the month, day and hour carry equal weight.