Lexeme is the term coined by Crystal to cover this, though it is not specific to inflections of nouns.
A lexeme is a unit of lexical meaning that underlies a set of words
that are related through inflection. It is a basic abstract unit of
meaning, a unit of morphological analysis in linguistics that
roughly corresponds to a set of forms taken by ...
Yes, folk means people, as in the English county names Norfolk and Suffolk, meaning the northern and southern people (of that region). It isn't listed in the dictionary as a plural of person because it's a different word with a similar meaning (just as cars isn't the plural of automobile).
You need to conjugate based on all the subjects of the sentence, you can't pick one and ignore the rest. Simply replace all the nouns with a single pronoun, and that will make it clear which conjugation you should use.
James and his family know - > They know
He and I are going -> We are going
I'm an Applied Mathematician. This is a Mathematics orientated question. I would recommend you post in the Maths 'Sister Page'. I will happily go into detail as to how each term is interpreted mathematically.
Please note that the mathematical definition of a given word is very often quite different from the standard English use (integrate, differentiate ...
Value is a countable noun:
a numerical quantity that is assigned or is determined by calculation or measurement
And that is what all of these uncountable numbers actually are!
So, in order to avoid vocabulary bloat, append the plural values to the class name, andyou get skewness values, kurtosis values, Fisher values, volatility ...
"Each" is always singular, therefore the grammatically correct sentence is "each two students shares one textbook."
This becomes obvious if you replace "two" with its synonym "pair of": "each pair of students share" is clearly incorrect.
The division between countable and uncountable nouns is not so strict and arbitrary for abstract nouns as you seem to have learned. When an abstract noun refers to a specific measurable quantity or quality, it is often possible to pluralize it, even if the noun normally is not used in the plural form.
"Volatilities" is not an impossible form; you can see it ...