Iceland theme
A line is controlled from opposite directions by two black line-pieces of the same motion. Black interferes with the line on both directions, and consequently White can give mate on a square on that line.
Paros, György
Die Schwalbe, Carte de Voeux TT, 1949
h#2 2.1... (5+9)
1.Sc4
Kd1
2.Bg4
d4#
1.Sg4
Kf1
2.Bc4
f4#