File 7 lets the cannon support a horse on the same flank and eye Black's weak points along the 7th line.

Five-Six or Five-Seven?

Five-Six is calmer; Five-Seven is more aggressive on the flank. Pick by temperament.

Five-Seven Cannon (Wu Qi Pao)

炮二平五，炮八平七

A flexible Central Cannon line where the left cannon aims at file 7, supporting a horse on the flank and preparing to pressure Black's position.

Five-Seven Cannon combines central control with a ready flank attack. It pairs well with 马八进七 and a later 车九平八.

Black answers 马8进7 + 马2进3, the usual solid reply.

Red plays 车九平八 to bring the left chariot into play.

Why file 7?: File 7 lets the cannon support a horse on the same flank and eye Black's weak points along the 7th line.
Five-Six or Five-Seven?: Five-Six is calmer; Five-Seven is more aggressive on the flank. Pick by temperament.

Central Cannon 炮二平五 Identical Cannons (Shun Pao) 炮二平五，炮8平5 Cross Cannons (Lie Pao) 炮二平五，炮2平5 Cross Palace Cannon (Guo Gong Pao) 炮二平六