Maybe <Infohunter> can weigh in on the distinction between the two.

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Maybe <Infohunter> can weigh in on the distinction between the two.>

I am more than delighted to answer the call. Just to make sure my response is impeccably accurate I consulted a reference book in my personal chess library, namely _The Oxford Companion to Chess_, ed. by D. Hooper and K.Whyld (1987). It has confirmed my thoughts on the subject. I also played over the four games mentioned above.

Now to particulars:

<FSR: <perfidious> I'm a little confused about the distinction between the two. If I understand the Wikipedia article's definition correctly, Plachuttas are a subset of Novotnys involving defensive pieces that move in the same direction (for example, a bishop and a queen that is defending a diagonal; or two rooks; or a rook and a queen that is defending a rank or file). Novotnys that are not also Plachuttas involve two different-moving pieces, such as a rook and bishop. I hope I've got that right.>

Well, no, that's not quite right. Novotnys are indeed interferences involving differently moving defensive pieces, but Novotny Interference is actually a subcategory of Grimshaw Interference, the difference being that in a Grimshaw the interference is not brought about by a sacrifice on the key square. Plachutta Themes also involve a sacrifice on the key square, causing similarly moving defensive pieces to interfere with one another. These are a subcategory of Wurzburg-Plachutta Themes, where no sacrifice on the key square is made. So it is correct to say that the Plachutta Theme is to the Wurzburg-Plachutta Theme as Novotny Interference is to Grimshaw Interference.

<perfidious: Reinfeld, in his annotations to the Tarrasch game, referred to the final move as the Plachutta theme.>

Novotný (he was Czech, not German) forces interference right away, because either line-mover cuts the other one's line.

Plachutta only overworks the one that captures (since both defenders move the same way). Thereafter, you need a 2nd sac to deflect it. So you need <two> sacs <and> a mate fork. In the Wikipedia examples, White has exactly that in all of the problems. (And then, given that your opponent might wish to just decline your 2nd sac, it follows that it, too, must be an else-it's-mate, i.e. you really need a <mate trident>.)

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This is Fuchs vs. Korchnoi. White's bishop provides a defense against ...Re1+, the rook on d2 provides a defense against ...Qxd6. By playing <25...Bd3>, Black shuts off both defenses. Captures on d3 by the bishop or rook restore their defense, but interfere with that of the other piece.

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This is Tarrasch vs. Allies. Here the c8 defends against Rxc5#, the d7 against Qb7+. By playing <31.Bc7>, White forces a capture which overloads the capturing piece by making it defend both threats. That's a Plachutta.

Which brings up an interesting question about the "similarly moving pieces" part. Suppose in Fuchs vs. Korchnoi, White had a queen on c4 instead of the bishop, a position like this:

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