Polonaises, Op. posth. (Chopin)

The Polonaises Op. posth[umous] include Frédéric Chopin's polonaises that were unpublished during his life.

The composer's first works were composed when he was seven years old; his father Nicolas Chopin published these works on behalf of his son. The Polonaises in G minor and B-flat major are among these posthumous pieces.

...
Wikipedia