It is possible to construct many elements simultaneously from general assignments such that the constructions do not suffer the forgetfulness property inherent in using the BUILD: command to contruct elements sequentially. As pointed out there, the components used to help construct elements for BUILD: commands are generally ``forgotten'' about once they have been used. With the COBUILD: command, the simultaneous construction means that the correct variances and covariances are constructed across the many elements built together. Generally, the COBUILD: command is used with assignments which include varying indices, and also with one-off components. The range of values for the indices actually to be used for the construction is set by either the INDEX: command or the INDEXVEC: command (depending upon whether the indices follow regular or irregular patterns respectively), and deleted by using the XINDEX: command.