Arimaa: A Chess Variant?

 A few days ago I found out about Arimaa (by accidentally clicking on a link to the Board Games shelf on Wikibooks), a board game designed to give humans an advantage over computers' sheer calculating power. After reading the rules, I doubt that it is really a chess variant, because the game mechanics are so completely different. Here are the (fairly simple) rules:

The game is played on a 8x8 board with the same number of pieces of each kind and number of piece types as in chess

    

Chess Piece	Arimaa Equivalent
Pawn	Rabbit
King	Elephant
Queen	Camel
Rook	Horse
Bishop	Dog
Knight	Cat

All the pieces move orthogonally one square (except for the pawn, which cannot move backwards), and higher ranking pieces freeze lower ranking pieces unless the lower ranking pieces have a friendly piece orthogonally adjacent. Higher ranking pieces can also push and pull pieces. 

How this works:

Push: Higher ranking piece moves an adjacent lower ranking piece once and occupies the square it left.

Pull: Higher ranking piece moves once, and a lower ranking piece that was adjacent to it before it moved occupies the square it left.

Captures only occur when a piece is in one of the "trap squares" (c3, f3, c6, f6) with no adjacent friendly piece. Captures often happen after a piece is pushed or pulled into a trap. 

The main rule that makes Arimaa possible is that each player moves four times during a turn.

This creates a very high branching factor and favors human strategical long term planning over brute force calculation - in theory. We'll get to that in a moment. The piece rankings are an important part of strategy, as each piece's ideal position is to freeze the piece one rank lower, allowing one's own piece of that lower rank to be unchallenged, if that makes any sense. 

Arimaa was created, as I mentioned earlier, as a challenge to board game engine developers, and that is why every year, starting in 2004, the strongest Arimaa engine played a challenge match. The developer of the first engine to defeat 3 humans would get $10,000. This 'Arimaa Challenge' was won in 2015 by David Wu and his program Sharp.