Answer:
You cannot write same elements in a set.
Step-by-step explanation:
In Set Theory, you cannot write same elements in a set.
Examples
A = {1,1} is not correct; the correct is A = {1}
B = {a,a,b,b,c,c} is not correct; the correct is B = {a,b,c}
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See for D = {m,a,t,h,e,m,a,t}
There are same m's, a's and t's.
The correct should be D = {m,a,t,h,e}
