Now all involved processes check these parameters against their own parameters and report an error in case of a mismatch. If the type is the same, for collective operations with a root process that rank and for reduce operations the reduction operation are also checked. The
error can only be detected for predefined reduction operation because it is impossible to verify whether the program code associated with a custom reduction operation has the same semantic on all processes. After this step depending on the operation different other parameters are also shared between the processes and checked.