Issue No.10 - October (1986 vol.35)
J.E. Smith , Astronautics Corporation of America
The paper by Schertz and Metze  is concerned with combinational circuits having a certain restricted fan-out structure. Two-level circuits have this restricted structure. A PLA as defined in  with only G and D faults behaves like a two-level combinational circuit with stuck-at faults. Hence, the results of Schertz and Metze are applicable. In an AND-OR PLA, a G fault is equivalent to a stuck-at-1 fault on an AND gate input, and a D fault is equivalent to a stuck-at-0 fault on an OR gate input. S and A faults are in a sense "duals" of G and D faults, and results concerning fault masking (and multiple-fault detection) for S and A faults in two-level circuits can be derived in a manner similar to G and D faults.
J.E. Smith, "Author's Reply", IEEE Transactions on Computers, vol.35, no. 10, pp. 931, October 1986, doi:10.1109/TC.1986.1676688