George Duke wrote on Wed, Sep 24, 2014 01:06 AM UTC:
No. NN x H is legal. There are several rationales. One, the capture is instantaneous. Two, given Harvester is compound of Bishop plus Gryphon counterpart stepping one as Rook first, the pathway of Harvester threatening check is only the one 'f4-f3-e2-d1'; and NN pathway is just as well e2-f3-f4. Three, there is only check on completion of turn.
A lot of these situations appear when stepping ordinary Bishop or Rook or Knight to capture the first fundamental piece Falcon. All it takes is conveniently placing one of those three lesser pieces R or N or B between own King and enemy Falcon. As they slide or jump to capture, technically there can be brief opening for three-path Falcon to be checking King. Yet it doesn't count until the turn ends, and then in comparable example to Harvester, the Falcon threatening is captured and gone.
Or using familiar Queen case, if you have WK-h1, WQ-h2, BQ-h8, obviously Qxh8 looks pretty good. White Queen is "pinned," loosely speaking, and cannot go along the other 3 directions, but she can capture the pinner.