Masked unguard of flight
An unguard of a flight‑square that is initially hidden because some piece occupies and masks the possible guard line; the unguard becomes effective only when that masking piece leaves the line allowing the king to step onto the now unguarded flight‑square.
Gadjanski, Borislav
Belgrade Internet Tourney TT-3, 2006
1st Prize
h#2 (5+12)
b) wSd4→c4
c) wSd4→d5
a) 1.Bxh4
Sb3+
2.Kc4
Rd4#
b) 1.Sxa2
Sd6
2.Kd5
Sb7#
c) 1.Rxd7
Sf4
2.Kd4
Sxe6#