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Thanks for the reference to Angel Chess. It is interesting that there the
concept 'protected' is also defined in terms of pseudo-legal moves (which
might put your King in check). My first idea was to use legal recapture as
the as the criterion, but that would force an engine to think one extra ply
ahead to determine legality after the recapture, and the effect would not
be that different. In fact pseudo-legal recapture is closer to Chu Shogi,
where it is perfectly legal (but of course losing) to leave your King in
check.

It is not clear to me if 'visually guarded' would include X-ray protectors.
With the rule I use, which measures this after the capture, they would
count. Otherwise the piece attacking its unprotected counterpart could be
attacked from behind on the same ray by a slider, after which trading would be possible.

Like in Chu Shogi, the rules I used also forbids indirect trading, so that
you cannot 'protect' your Lion by launching a counter attack on his Lion
(or soft-pin the piece he attacks you with on his Lion).


As to the name, it still seems 'Cannonized Chess' would have been a more
apt name for the other game, as there are 2 other exo-pieces apart from
Leo. But I am also happy with Mighty-Lion Chess, so I will use that name in WinBoard/Fairy-Max.

Note that the double move of the Lion only manifests itself when the first
leg was a capture, because every possible destination can also be used
through a direct leap. And in that case it has the character of e.p.
capture: a piece disappears on a square other than the to-square. Compared
to regular e.p. capture the to-square isn't necessarily empty (a
complication that also strikes Alice Chess), so that you can have two
capture victims.