PDB Server - Keyword Definition


Help retractor

Before 1923, when Høeg published his first 'retromate', Retractor was well defined: some retroplay followed by an ordinary forward stipulation; in the retroplay all legal retractions were allowed, but in a correct Retractor only one retroplay would enable the forward stipulation, which could be #n, s#n, or h#n with n specified.
These are all termed "Help Retractors" not because the forward stipulation is helpmate in 1, but because the two camps help each other in the retroplay. This risks being confusing if in a problem the retroplay is just one white retraction and the forward stipulation is #2!
By contrast, in a Defensive Retractor (e.g., type Høeg, Proca, or more recently Klan) the camps fight against each other in the retroplay.

Rétracteur aidé