Assign one function to another. The functions must reside in the same type of FunctionSpace. One or both functions can be sub functions.
Assign several functions to sub functions of a mixed receiving function. The number of receiving functions must sum up to the number of sub functions in the assigning mixed function. The sub spaces of the assigning mixed space must be of the same type ans size as the receiving spaces.
Assign sub functions of a single mixed function to single receiving functions. The number of sub functions in the assigning mixed function must sum up to the number of receiving functions. The sub spaces of the receiving mixed space must be of the same type ans size as the assigning spaces.