I’ve read up on Babson tasks, and they mention that all known tasks are not perfect because there are duals. I’m not sure what this means exactly. What precisely is a “dual” in chess problems?

  • The definition of “dual” for a direct mate is clear enough. An interesting follow-up question is: how tolerated are they, in different kinds of composition? – Laska Nov 30 '20 at 3:22
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    Perhaps so, @Laska, perhaps so. Not that I need it anytime soon, of course. :-) – Rewan Demontay Nov 30 '20 at 3:48

A dual is an alternate solution, other than the intended one, after the first move of a problem or study. If it happens on the first move, the problem or study is called cooked instead.


Ideally, White should have only one move at each juncture that solves a problem. If White has an alternative at any stage other than the first move, this is a dual. A dual is not as serious a flaw as a cook, and in minor lines, duals may be permissible (opinions differ on this point). Some problems make a virtue out of dual avoidance – of two apparently equivalent white moves, only one works.

(source: Wikipedia)

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