Think of this ob as saying "the entire move is only valid if this stop along the way is at the edge of the board, and the next one (if any) is not."
Yes, but this is what oab... says now, make a move that leaves the board, and in the next leg step back onto it. The Reflecting Bishop (for a single reflection) is yafoabyasB. To the edge, one more step back and forthe to test whether you ran into it, and then continue again as slider in the perpendicular direction. [B-oF-bF-sB] in bracket notation. I gues even [oB-bF-sB] would do (but would generate moves in duplicat when already on the edge).
Yes, but this is what oab... says now, make a move that leaves the board, and in the next leg step back onto it. The Reflecting Bishop (for a single reflection) is yafoabyasB. To the edge, one more step back and forthe to test whether you ran into it, and then continue again as slider in the perpendicular direction. [B-oF-bF-sB] in bracket notation. I gues even [oB-bF-sB] would do (but would generate moves in duplicat when already on the edge).