1. He is extremely strong — not but that he will catch cold at times.

2. Possibly not, but that is the rigorous mathematical answer to your question.

3. Not but that he believes it himself.

4. He is very strong - not but that he will catch cold sometimes.

5. I cannot do it, not but that a stronger man might.

6. I cannot do it not but that a stronger might.

7. The boy is very healthy -- not but that he will catch colds sometimes.