Have I found a Triple Check Position?
I have often wondered why there is no mention of triple checks in classical chess. Then, I came across a novel point for this chess position evaluation program I am (still) writing. First, though, I will present a couple of facts that every chessplayer will already know; but, is relevent to the discussion of triple checks.
Any chessplayer knows that his King can be put in check by a single enemy unit. This can be demonstrated by getting out the chessboard and placing the WK on g1, a WB on e4, and the BK on e8. (I am presenting the board with just the basic pieces to illustrate the point.) The move Be4-g6+ puts the BK in check. This is a single check, as the BK can only be taken by the WB on g6 next move.
Okay, same starting position as before, adding a WR at e1. Now, the move Be4-g6+ is a double check. (It is also a discovered check.) The BK was not in check by the WB at e4 nor the WR at e1 before the move; but, after the move either White piece can capture the BK next move. The BK has two pieces attacking him at the same time.
Now, getting to my point about triple checks. The pieces on the board are WB at e4, WR at e3, WR at e1, and BK at e8. When the WB moves, Be4-g6+, that is one check to the BK. The move also clears a path for the WR at e3 to check the BK. Since the two WRs are positioned on the same file, with no piece between them, doesn't the WR at e1 cover the same squares as the WR at e3? If the WR at e3 is giving check, isn't the WR at e1 also giving check, too? I think so, so I now believe that I have a triple check! What do you think?
(I came across this thought as I was writing the subroutines to count the squares the pieces could move to. Which squares that they could reach, and which pieces they added their coverage beyond. Let's consider an example: the two WRs above. Starting with the WR at e1, the square e1 is covered only by the WR at e3. The square e3 is covered only by the WR at e1. The squares e2, e4, e5, e6, e7, and e8 are covered by both WRs. e8 is the end of their influence, not only because it is on the edge of the board; but, also because the piece on e8, the BK, if it were on another square would stop their range. They do not add their power to the BK piece, so it stops there.)
Using the same agrument I have for triple checks, I then thought about could there be quadruple checks. And, indeed, I thought of an example. BK on e8, BP on f7, WB on e6, WR on e3, WR on e1, WQ on h5, and WK on g1. The move Be6xf7+ makes the quadruple check. The two WRs, e1 and e3, the WB, f7, and the WQ on h5.
There is also one for quintuple check: BK on e8, BR on f7, WP on e6, WB on g6, WQ on h5, and WK on g1. The move e6xf7 would make the quintuple check. Check along the e8-h5 diagonal by the WP on f7, WB on g6, WQ on h5. Check by the two WRs, e3 and e1.
While I think that triple check would occasionally occur in real games of chess, I have my doubts that quadruple and quintuple checks would. I could not think of an example position that would result in a sextuple check. (Check by six times.)