>"If all squigs are squalls and all squalls are zigs, are all squigs zigs?"
>Yes. No external unstated context required.
Only if you assume that squigs really are squalls and that all sqalls really are squigs. This is without mentioning that you must assume that the meaning of all those words was the intended meaning, as well as assuming that they are not lying, as well as assuming that inference always yields a true answer, as well as the assumption that the universe is consistent with itself, as well as... the assumptions are endless.
>"Cost" (verb): to require the payment of (money or something else of value) in an exchange.
First of all, your overly narrow definition isn't even syntactically correct. What kind of bullshit source, which you failed to cite by the way, are you taking that from? The shopkeep at no time requests a dollar, as written.
>Further, "anyone who is talking" is talking about what they are talking about.
You have to know something to try and communicate it, even if you only know that you do not know.
>The CONCEPT of knowledge. Knowing. Not the application of information which obviously must be used to communicate.
Are you arguing that information is not included in the definition of knowledge? Because that would be full-on retarded.
>And finally, just because one currency is mentioned, does not mean that all prices and costs are in the currency.
It does if you demand that we disregard external information, as you did. The problem states the existence of one and only one currency. Unless you assume external information, dollars are the only unit of currency and thus is the only possible unit which the answer could use.
>"Assumptions" are fine, when they have a logical basis.
Yes, but logical basis is not "proof" the way you seem to like to use it. All logic requires further assumptions... if you go far enough back into your reasoning, there is some assumption with no logical reasoning.