I don't think he was treating "all marbles are white" as the negation of "all marbles are black".
The comment he replied to was claiming that any question that is true for n = 1 should also be true for n = 0, but this comment shows that it is obvious nonsense.
The comment above basically claimed:
marbles = ["black"]
all(m=="black" for m in marbles) # => True
marbles.pop()
all(m=="black" for m in marbles) # => True
If that is the case then the following would also need to be true:
all(m=="white" for m in marbles) # => True
all(m=="green" for m in marbles) # => True
What color is the marble?
Just because the question “there is a marble in the bag such that…” is false does not mean you can just negate it and say “all marbles in the bag are…” if the actual answer is that the question is not applicable.
The comment he replied to was claiming that any question that is true for n = 1 should also be true for n = 0, but this comment shows that it is obvious nonsense.
The comment above basically claimed:
If that is the case then the following would also need to be true: What color is the marble?Just because the question “there is a marble in the bag such that…” is false does not mean you can just negate it and say “all marbles in the bag are…” if the actual answer is that the question is not applicable.