Supremum and infimum being the endpoints

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Say we have the set $[1,5]$, this being a closed set, we know the infimum of supremum of this set is inside the set. Shouldn't the supremum in this case be $5$ and the infimum be $1$? Also in general, in a closed set [a,b], can we say supremum and infimum be $b$ and $a$ respectively?