How To Do It

0,0,1,0,0,0

0,0,0,0,0,0

Presence or Absence of Carry

Must Be Detectable

0,0,1,1,0,0

0,0,0,1,0,0

Carry Must Be Tested In Both

States

Unacceptable Substitute For Test 2!

0,0,1,1,1,0

0,0,0,1,1,0

Error Is Masked, Because C2 and

C3 are Identical in Both Tests

Test 1

Test 2