 Equivalence is not to be confused with functional correctness, which must be determined by functional verification.The initial netlist will usually undergo a number of transformations such as optimization, addition of Design For Test (DFT) structures, etc., before it is used as the basis for the placement of the logic elements into a physical layout.Contemporary physical design software will occasionally also make significant modifications (such as replacing logic elements with equivalent similar elements that have a higher or lower drive strength and/or area) to the netlist.