Hễ giải mã là chúng ta ghi dãy số.

This is a common Vietnamese pattern meaning something like whenever ... then ..., as soon as ..., or if ever ... then ....

So in Hễ giải mã là chúng ta ghi dãy số, the structure is:

• hễ = whenever / as soon as
• ... là ... = then ...

A very literal breakdown would be:

• Hễ giải mã = whenever decoding happens / whenever we decode
• là chúng ta ghi dãy số = then we write down the number sequence

So hễ ... là ... often expresses a regular reaction or automatic consequence.

No. In this sentence, là is not really the normal to be verb.

In the pattern hễ ... là ..., là works more like then or a marker introducing the result/main clause.

So:

• Hễ A là B ≈ Whenever A happens, B happens
• not A is B

This is a very important point, because learners often first meet là as to be, but Vietnamese uses it in several other ways too.

Vietnamese often omits subjects when they are understood from context.

Here, giải mã just means decode / decipher. The sentence does not explicitly repeat the subject in the first clause. In context, the understood subject is probably the same group later referred to by chúng ta.

So the sentence can be understood as something like:

• Whenever we decode, we write down the number sequence

Vietnamese does this kind of omission much more freely than English.

A fuller version could be:

• Hễ chúng ta giải mã là chúng ta ghi dãy số.

But repeating chúng ta twice may sound heavier than necessary if the subject is already clear.

Giải mã means to decode, to decipher, or to crack a code/message/system.

It is made of:

• giải = to solve, untie, unravel
• mã = code

Together, giải mã is used for things like:

• decoding a secret message
• deciphering a code
• interpreting encrypted information

Depending on context, English translations may vary slightly, but decode is the most direct match.

Ghi means to write down, to note, or to record.

In this sentence, ghi dãy số means write down the sequence of numbers or record the number string.

Compared with viết:

• viết = to write
• ghi = to write down / note / record

So ghi often sounds more like making a note of information, which fits well here. If someone decodes numbers and notes them down, ghi is very natural.

Dãy số means a sequence of numbers, a series of numbers, or a string of numbers.

Breakdown:

• dãy = row, line, series, sequence
• số = number

So ghi dãy số means writing down a set of numbers in order.

Depending on context, English could be:

• write down the number sequence
• record the string of numbers
• note the series of numbers

Chúng ta means we, including the listener.

Chúng tôi means we, excluding the listener.

So if the speaker says:

• chúng ta = you and I / all of us including you
• chúng tôi = my group, not including you

In this sentence, chúng ta ghi dãy số suggests the speaker includes the listener in the action of writing down the numbers.

That is an important distinction in Vietnamese and one that English does not usually mark.

Vietnamese does not mark tense the same way English does. This sentence has no explicit tense marker, so the time is understood from context.

Because of hễ ... là ..., the sentence most naturally sounds:

• habitual: Whenever we decode, we write down the number sequence
• procedural/instructional: As soon as we decode, we write down the number sequence

So it can describe:

• a general rule
• a routine
• a repeated action
• a step in a process

If the speaker wanted to make time clearer, they could add words like:

• đã for past context
• sẽ for future context
• đang for ongoing context

But none of those are necessary here.

It can suggest either, depending on context, but the structure strongly leans toward a rule-like or repeated relationship.

With hễ ... là ..., Vietnamese often expresses something like:

• whenever this happens, that happens
• as soon as this condition is met, that action follows

So the sentence could mean:

• a regular procedure: every time decoding happens, we write the numbers down
• an immediate next step: once decoding happens, we write the numbers down

Context tells you which reading is intended.

Yes, depending on the nuance.

Possible alternatives include:

• mỗi khi = whenever / every time
• cứ ... là ... = whenever ... then ... / every time ... then ...
• khi = when

For example:

• Mỗi khi giải mã, chúng ta ghi dãy số.
• Cứ giải mã là chúng ta ghi dãy số.

Compared with these:

• hễ often has a slightly more fixed whenever/as soon as feel
• cứ ... là ... is also very common for repeated cause-and-result
• mỗi khi sounds straightforwardly like every time

All are possible in the right context, but hễ ... là ... is a very recognizable pattern.

Very often, yes, especially in the set pattern hễ ... là ....

The là helps clearly introduce the result clause. Without it, the sentence may still be understandable in some contexts, but the classic structure is:

• hễ + clause + là + clause

So learners should treat hễ ... là ... as a chunk.

That said, Vietnamese has many flexible sentence patterns, and in casual speech people may shorten things. But for learning purposes, keeping là here is the safest and most natural choice.

It is understandable, but it does feel somewhat compressed or context-dependent.

The first clause Hễ giải mã omits the subject, which is normal in Vietnamese if context is clear. Still, in isolation, some speakers might expect a slightly fuller sentence such as:

• Hễ giải mã được là chúng ta ghi dãy số.
• Hễ giải mã xong là chúng ta ghi dãy số.
• Hễ chúng ta giải mã được thì chúng ta ghi dãy số.

Those versions make the relationship a little more explicit:

• giải mã được = successfully decode
• giải mã xong = finish decoding
• thì = then

So the original sentence is not wrong, but it relies on context and sounds a bit concise.