  We introduce a general construction on 2-monads. We develop background on
maps of 2-monads, their left semi-algebras, and colimits in 2-category. Then,
we introduce the construction of a colimit induced by a map of 2-monads, show
that we obtain the structure of a 2-monad and give a characterisation of its
algebras. Finally, we apply the construction to the map of 2-monads between
free symmetric monoidal and the free cartesian 2-monads and combine them into a
linear-non-linear 2-monad.
