We can say: The expression, “B can continue the series”, is used under different circumstances to make different distinctions. Thus it may distinguish a) between the case when a man knows the formula and the case when he doesn't; or b) between the case when a man knows the formula and hasn't forgotten how to write the numerals of the decimal system, and the case when he knows the formula and has forgotten how to write the numerals; or c) (as perhaps in 64)) between the case when a man is feel-
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ing his normal self and the case when he is still in a condition of shell shock; or d) between the case of a man who has done this kind of exercise before and the case of a man who is new at it. These are only a few of a large family of cases.