Either a masked channel or a veto bit rejects the event. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
A masked candidate cannot pass
A candidate on a masked channel has candidate-enabled bit 0.
A=0×(1−0)=0
A veto rejects an otherwise enabled candidate
An enabled candidate with veto bit 1 has accepted bit 0.