t-Fault t/2-step sequentially diagnosable systems

Fault diagnosis is considered for systems comprising n units u
0
, u
1
,...,u
n-1
in which u
i
tests u
i+1
and u
i+2
. A necessary and sufficient condition for the diagnosability of t faults in t/2 or t/2 + 1/2 steps is stated, the condition taking the form of an inequality relating n and t.