Hello native English speakers.
What is difference between these two sentences?

1a. You can not smoke here.
1b. You can't smoke here.
2a. You may not smoke here.
2b. You mayn't smoke here.

Question:
Which is grammatically correct?
Do they have the same meaning?

Question

Hello native English speakers.
What is difference between these two sentences?

1a.   You can not smoke here.
1b.   You can't smoke here.
2a.   You may not smoke here.
2b.   You mayn't smoke here.

Question: 
Which is grammatically correct?
Do they have the same meaning?

Answer

Hello, in this sentence to express that smoking is prohibited here, we use the negative form of 'can', which is 'cannot', with no space. The other three sentences are gramatically correct, however 'mayn't' is rarely used nowadays as the negative form of 'may'. Saying 'you may not smoke here' is slightly more formal than 'you cannot smoke here'. Contractions such as 'can't' are more common in spoken, everyday language, whereas the full form 'cannot' is more emphatic.

P.s. 'can not' would be used in a sentence with two clauses such as 'I can not only see it, but hear it'.

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