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I came around this one just now and I can't tell the meaning of this sentence by the context.

no new vehicle is used unless all but at most one other vehicle has at least 50% of its time scheduled

Does it mean something like "all are, but one is not"?

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I suppose it means there is never more than one vehicle with 50% or less of its time scheduled, am I right ? – tesseract Jan 24 '12 at 23:49
This is turgid sprinting-through-chewing-gum prose. Yecch. What is wrong with the author, who does not know the difference between its and it's? I feel sorry for you, poor tesseract, who has to read such sorry gobbledegook. – ncmathsadist Jan 24 '12 at 23:51
+1 for bringing us such a laughable example of poor writing. D- ;) – ncmathsadist Jan 24 '12 at 23:53
I think it means a new vehicle is not used if two or more others are more than 50% free. – FumbleFingers Jan 25 '12 at 0:00
...perhaps the writer is a fan of Bertrand Russell, whose note to the milkman said In general, please leave a set of bottles equal in number to the set of empty bottles on the step, except where the latter set is null, in which case leave one bottle, reducing by that number the delivery on the next occasion if and only if two or more bottles are present. – FumbleFingers Jan 25 '12 at 0:05
up vote 8 down vote accepted

"At most one" means zero or one.

"All but at most one" means "all" (all minus zero) or "all but one" (all minus one).

But wow, what a confusing sentence!

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Thank you very much :) – tesseract Jan 25 '12 at 0:07
Think of "all but one", and then allow for the case of zero. "All but at most one". But wow, awkward wording. – Jay Jan 25 '12 at 3:22
This is the right answer. Another confusing wording to look out for: "At least one and at most one" = "exactly one". – shane Oct 15 '14 at 11:48

if this had been read aloud by the author before publishing it may have been revised to say: "No new vehicle is used until only one remains unused."

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Thanks for clarifying this :) – tesseract Jan 25 '12 at 0:08
Ah, but that would leave unspecified the matter of exactly what "unused" means. I sense your job doesn't involve writing fleet management rule books! :) – FumbleFingers Jan 25 '12 at 2:15

for example, x=0 at all but at most one point in (a,b) means all the x are zeros except at most one point in (a,b) may be non-zero.

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This is even more confusing than the OP's original statement. – Matt E. Эллен Oct 15 '14 at 11:54

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