Hello my brother
unluckily, I have not found any thing related to the useage of these two words
I looked for the diifrence in three sourses
But of no result
any way
In my opinion the diffrence is in the formality of the usage
I .e
I have only three books
To limit an amount of something
when you want to end your speech
I.E
Thats what I want to say only
********
Just
Is more formal I think
Its mostly used in present perfet
I have jast come
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