f : A---> A
∣A∣ = n
The first element of the domain has n choices for mapping,2nd element has (n-1) ,3rd element has (n-2) choices and so on.
So, total number of one-to-one functions = n ⨉(n-1)⨉(n-2)⨉(n-3).........⨉1 = n!
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Yeah ! Of course.IT people are also ...