هل verb to be+ المصدر يساوى must

اذا كنت تقصد المصدر infinitive علي انه to +base verb فانت علي صواب وان كنت تقصد المصدر اي base verb فيجب اضافة to قبله اي ان -وباختصار- :
be to + infinitive = must/should

FORM
When we write about future obligations, we can use a formal pattern composed of two elements
the verb to be in the present tense conjugated to match the subject + the infinitive of the main verb
TO TRAVEL, AS A FUTURE OBLIGATION
Affirmative Negative Interrogative Negative Interrogative
I am to travel. I am not to travel. Am I to travel? Am I not to travel?
You are to travel. You are not to travel. Are you to travel? Aren't you to travel?
He is to travel. He is not to travel. Is he to travel? Isn't he to travel?
It is to travel. It is not to travel. Is it to travel? Isn't it to travel?
We are to travel. We are not to travel. Are we to travel? Aren't we to travel?
They are to travel. They are not to travel. Are they to travel? Aren't they to travel?
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FUNCTION

In written English, we can use this pattern to refer to an obligation or requirement that we do something at a time later than now. It is similar in meaning to must, but there is a suggestion that something has been arranged or organised for us. It is not normally used in spoken English.
EXAMPLES
.................................................. ..........
 You are to leave this room at once, and you are to travel by train to London.
 In London you are to pick up your ticket from Mr Smith, and you are to fly to your destination alone.
 When you arrive, you are to meet our agent, Mr X, who will give you further information.
 You are to destroy this message now.

We are to / we are not to

I've been living in the US for a few months and I've had opportunity to read some articles and books more easily. But I've had doubts about some constructions. I wonder how it is that is to used in these sentences:


Roger Woodham replies:


he is to / they are to

We use this structure quite a lot to talk about official plans and arrangements. In your examples, Enrique, the verb be is omitted which is very characteristic of newspaper headlines. In any text follow the headline it would need to be included, e.g.

The British Prime Minister, the French President and the German Chancellor are to meet in Berlin this weekend.

Note that we can also use this structure as a perfect infinitive to describe a planned event that did not take place:

The British PM was to have had talks with his Canadian counterpart on his way to the US, but these were cancelled when the trip was curtailed. I was to have gone on holiday with Ruth, but she couldn't get time off work.

In a more informal register, was supposed to has a similar meaning:

I was supposed to go on holiday with Ruth, but she couldn't get time off work.

you are not to – I am to

Note that this structure can also be used to issue or to acknowledge instructions or orders. When it is used in negative sentences, it nearly always has this meaning, but it can be used in affirmative sentences with this meaning too

We are to smoke only in the designated areas. We are not to smoke anywhere else.

We are to look after our neighbours’ dog while they are away but we’re not to feed him any chocolate. Else he will be sick.

There is future meaning here, but it also means at any time, particularly in negative sentences. As we are acknowledging an instruction, we could also use we mustn't in these sentences instead of we’re not to.

Here are some more examples of this usage. Look at these instructions to members of a youth club in an inner-city area:

1 Respect yourself and other members.
2 No scrapping or fighting and no weapons.
3 No bullying, cussing or dissing.
4 No setting off fire alarms unless there is fire.
5 No climbing on the roof.
6 Entrance through front door only, not back door.

We can re-phrase these instructions, using are to / are not to. We can also use be permitted to or be allowed to as an alternative to mustn't as the obligation is imposed externally. (I have also tried to paraphrase youth-culture vocabulary in this re-wording):

1 You are to respect yourself and other members at all times.
2 There is to be no scrapping or fighting and no weapons of any kind are permitted.
3 You mustn't bully anyone and you are not allowed to swear at anyone or insult other members.
4 Fire alarms are not to be set off unless there is fire.
5 Climbing on the roof is not permitted.
6 You are to enter the youth club only through the front door, not through the back entrance.

We are to read what is written.