The molecular structure has to be well defined. Execution of the patch statement destroys fragile atom selections (Section 2.15); e.g., the atom properties (Section 2.16) are conserved during patching, except for the internal stores (STORE1, STORE2, ... ). The atom properties of additional atoms are set to default values. Other information, such as information for the xrefin or NOE statements, is lost during patching.