Hễ tôi hoàn trả bản in là thủ thư kiểm tra.

Hễ ... là is a pattern meaning whenever / every time / as soon as.

In this sentence:

• Hễ tôi hoàn trả bản in = whenever I return the printout
• là thủ thư kiểm tra = the librarian checks it

So hễ introduces the repeated condition or trigger, and là introduces what happens as a result.

A useful way to think of it is:

• Hễ X là Y = Whenever X happens, Y happens

This pattern often suggests something happens regularly or without exception.

No. In this sentence, là is not the normal copula meaning to be.

Here, là is part of the pattern hễ ... là ..., where it links the first clause to the result clause. In English, you might translate it as:

• then
• it is that
• or often just leave it untranslated

So:

• Hễ tôi hoàn trả bản in là thủ thư kiểm tra. = Whenever I return the printout, the librarian checks it.

You should learn là here as a structural marker, not as the verb to be.

Yes, but it has a slightly marked feel compared with some other options. It often sounds like:

• whenever
• any time that
• every single time that

It can feel a bit emphatic, as if the result happens very consistently.

Other common ways to express a similar idea are:

• Mỗi khi tôi hoàn trả bản in, thủ thư kiểm tra. = Every time I return the printout, the librarian checks.
• Cứ tôi hoàn trả bản in là thủ thư kiểm tra. = Whenever I return the printout, the librarian checks.

Compared with those:

• hễ often sounds a little more like as soon as / whenever at all
• mỗi khi is often the most neutral way to say every time
• cứ ... là ... is also very common for repeated cause-result patterns

Hoàn trả means to return something, especially in a somewhat formal or administrative style.

It is understandable here, but many learners should know that in everyday speech Vietnamese speakers often use simpler verbs such as:

• trả
• trả lại

So these are close in meaning:

• hoàn trả bản in
• trả lại bản in
• trả bản in

Using hoàn trả can sound more formal, more written, or more official.

So if you are speaking casually, trả lại may sound more natural in many contexts.

Bản in means a printed copy, printout, or printed version.

Breakdown:

• bản = a copy/version/document item
• in = print / printed

Together, bản in means something like:

• a printout
• a printed document
• a printed copy

So it is not just any book or paper. It specifically refers to something that has been printed.

Examples:

• Tôi làm mất bản in. = I lost the printout.
• Bạn có thể đưa tôi bản in không? = Can you give me the printed copy?

Vietnamese does not use articles like English a / an / the.

So thủ thư can mean:

• a librarian
• the librarian

The exact meaning depends on context.

In this sentence, because the situation sounds specific and the meaning is already known, English often uses the librarian. But Vietnamese itself does not need a separate word for the.

This is very common:

• giáo viên = teacher / the teacher / a teacher
• bác sĩ = doctor / the doctor / a doctor
• thủ thư = librarian / the librarian / a librarian

Vietnamese often leaves out an object when it is already understood from context.

Here, kiểm tra means check / inspect, and the omitted object is probably something like:

• bản in
• or the returned item
• or the return itself

So the full meaning is something like:

• Whenever I return the printout, the librarian checks it.

Vietnamese does this a lot when the object is obvious.

You could make it explicit:

• Hễ tôi hoàn trả bản in là thủ thư kiểm tra bản in.

But that may sound repetitive if the listener already knows what is being checked.

Vietnamese usually puts the condition / trigger first and the result second in patterns like this.

So the structure is:

• Hễ + clause 1 + là + clause 2

Here:

• clause 1: tôi hoàn trả bản in
• clause 2: thủ thư kiểm tra

This is very natural for expressing:

• whenever X happens, Y happens
• as soon as X happens, Y happens

English can also do this with similar order:

• Whenever I return the printout, the librarian checks it.

Yes. Several alternatives are possible, depending on style and nuance.

Some common rewrites:

• Mỗi khi tôi hoàn trả bản in, thủ thư kiểm tra. = Every time I return the printout, the librarian checks it.
• Cứ tôi hoàn trả bản in là thủ thư kiểm tra. = Whenever I return the printout, the librarian checks it.
• Khi tôi hoàn trả bản in, thủ thư kiểm tra. = When I return the printout, the librarian checks it.

Differences:

• hễ ... là ... = strong repeated trigger/result
• mỗi khi = neutral every time
• khi = can simply mean when, sometimes less strongly repetitive
• cứ ... là ... = very common for repeated patterns

It normally suggests repeated events.

That is because hễ ... là ... usually means:

• every time
• whenever
• any time that

So the sentence does not usually mean one single return and one single check. Instead, it means this is the regular pattern:

• whenever I return the printout, the librarian checks it

If you wanted to focus on one specific event, Vietnamese would usually choose a different structure.

Sometimes learners will see related patterns with thì, but in this sentence the given structure is hễ ... là ..., which is a standard pattern.

You may encounter:

• Hễ ... là ...
• Cứ ... là ...
• sometimes other conditional-style patterns with thì

For this sentence, it is best to learn hễ ... là ... as a chunk.

So a good learner rule is:

• hễ ... là ... = whenever X, Y

Even if other variants exist in real usage, this is the safest way to understand the sentence you were given.

In this sentence, thủ thư is a normal noun meaning librarian.

Vietnamese job words can be used very simply without articles:

• thủ thư kiểm tra = the librarian checks

Depending on context, profession words can also sometimes function almost like forms of address, but here it is just the subject of the sentence.

So the grammar is straightforward:

• thủ thư = subject
• kiểm tra = verb

In many everyday contexts, yes.

A native speaker often prefers shorter, less formal wording in speech. For example:

• Hễ tôi trả lại bản in là thủ thư kiểm tra.
• Mỗi khi tôi trả bản in, thủ thư kiểm tra.

If the setting is official, written, or administrative, hoàn trả is perfectly possible. But for casual conversation, trả or trả lại is often more natural.

So a useful learner takeaway is:

• hoàn trả = correct, formal
• trả / trả lại = more everyday