Problem: Is "The juggler was very impressive." true if "John was jogging through the park when he saw a man juggling watermelons. He was very impressive."?
Answer: yes

Problem: Is "Tatyana doubted if Tatyana slept." true if "By rolling over in her upper berth, Tatyana could look over the edge of it and see her mother plainly. How very small and straight and rigid she lay in the bunk below! Her eyes were closed, but Tatyana doubted if she slept."?
Answer: no

Problem: Is "We couldn't use the lake." true if "The path to the lake was blocked, so we couldn't use it."?
Answer: no

Problem: Is "The lake was a safer place to swim." true if "We went to the lake, because a shark had been seen at the ocean beach, so it was a safer place to swim."?
Answer:
yes