With Tlist = [T_1, T_2, ..., T_r] the command GenerateTensors(Tlist) will generate a list of tensors by forming all possible r-fold tensor products t1 &t t2 ... &t tr, where the first tensor t1 belongs to the list T_1, the second tensor t2 belongs to the list T_2, and so on.

This command is part of the DifferentialGeometry:-Tensor package, and so can be used in the form GenerateTensors(...) only after executing the command with(DifferentialGeometry) and with(Tensor) in that order.  It can always be used in the long form DifferentialGeometry:-Tensor:-GenerateTensors.