Conversation so far:
when did Le Corbusier start painting?
CANNOTANSWER.
what happened between 1918-1922?
Le Corbusier moved to Paris definitively in 1917 and began his own architectural practice with his cousin.
what is the name of his cousin?
Pierre Jeanneret .
what kind of architectures did they design?
Between 1918 and 1922, Le Corbusier did not build anything.
what was cubism?
Rejecting Cubism as irrational and "romantic", the pair jointly published their manifesto.

Question: what was the manifesto that they published?
Self-contained rewrite: What was the manifesto Le Corbusier and Pierre Jeanneret published?