So I've tried to translate two sentences, each with the predicates:
$B(x,y): x\text{ beats }y$
$F(x): x\text{ is a football team}$
$Q(x,y): x\text{ is a quarterback for } y$
$L(x,y): x\text{ loses to }y$
$c: Wildcats$
$j: Jayhawks$
I suddenly became a bit nervous about the translations, and had some questions about my translation.
- Every football team has a quarterback $$\forall x(F(x)\to \exists y(Q(y,x))) $$ My predicate logic formula would translate to: "For all football teams, there exists a quarterback". Should I use $\to$ or should I translate it with an $\land$ instead. Another question is couldn't this be understood as if all the football teams had the same quarterback?
- The Wildcats beat some team, which beat the Jayhawks $$\exists x(F(x)\land B(c,x)\land B(x,j))$$ Is this an okay translation or should I use implies?
After reading the book it seems like $\to$ is used frequently if not always with the universal quantifier $\forall$, while $\land$ is used when we have the existential quantifier $\exists$. Is this pattern true? I've never seen anyone mention it, and there is nothing of it in the book. Is there a good way to phrase the translation, that it might be clearer if it should be $\land$ or $\to$?
The question about the singularity or multiplicity of the existential quantifier. How should I differentiate between:
- It is one and the same quarterback for all football teams
- All football teams have one quarterback,
- All football have some who are their quarterback (a group of quarterbacks who all are quarterbacking for all teams)
- All football have some who are their quarterback (each football team has their own group of quarterbacks)
When searching for the answers it seems like there is the quantifier $\exists !$ which should only mean one, but that is not part of the language I've been taught.
With respect to the last part of your question, i have tried and answered them here
You can use the $\exists!$ quantifier, which reads as "there exists a unique". You can read more here, which shows how to represent the symbol in the symbols you are "allowed" to use.