Sky cannon, earth cannon
天地炮 pairs two cannons: the sky cannon holds the centre file, pinning the middle advisor through Black's own centre pawn; the earth cannon sinks to the far bottom line, ready to fire along the back rank. Between them every defender is frozen — and with the general glaring up the f-file, the chariot has a door to slam. Its landing square is covered by three gunsights at once: the general's file, the earth cannon through the chariot itself, and the sky cannon's pin on the advisor. Black is frozen solid — close heaven and earth on him.
Solve the challenge to finish this lesson.