How many "gaps" is needed in a predicate?

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So, this actually builds on an earlier post where I asked which of the two expression of PL best express the sentence "Stockholm is the largest city in Sweden":

Is it:

$$Cab \space\ \wedge \forall x((\neg x=a \wedge Cxb) \rightarrow Lax)$$

with this key:

a: Stockholm

b: Sweden

Lxy: x is larger than y

Cxy: x is a city in y

or is it

$$ Ca \space\ \wedge \forall x((\neg x=a \wedge Cx) \rightarrow Lax) $$

with this key:

a: Stockholm

Cx: x is a city in Sweden

Lxy: x is larger than y

Now, from the feedback I got, it seemed that the difference didn't matter that much - some liked the first better, while others liked the second the best. (There was also some talk about difference in "sorts", but I haven't encountered that before).

I opted for the second one because of simplicity, but when I talked to my teacher now he said he was disapointed because I didn't choose the first, because "you must remember to always have as many gaps possible in a predicate" ... So, my question is: Is that really a "rule" in Predicate Logic? (the background here is that I was sooo close to getting 100% in logic, and then I lose marks because of this (and one similar) exercise, which is very annoying!)

Thanks!

Solved: I talked to my teacher and she let me keep the marks although she said she prefers to formalise as much information as possible.