Premise:
"That always seems the difficulty to me." Poirot shook his head energetically. "
Hypothesis: Poirot nodded.

no

Premise:
"As a result of these activities, the Medicare"
Hypothesis: There were no activities to extrapolate results from.

no

Premise:
"Hall is unapologetic about his spying, but the lack of living witnesses makes prosecution impossible."
Hypothesis: Living witnesses play a key role in being able to prosecute a suspect.
yes