Create a function that accepts an array of string as an input and returns Array list of repetitive items.

Ex$1$ : input : $["$ali$",$ "simranjit", "vansh", "ali","tamanna", "simranjit"$]->$ Output : $["$ali$",$ "simranjit"$]//$ ali and simranjit repetead more than once in input but tamanna and vansh was only once

Ex$2$: input : $["$david$",$ "alex","robert","David", "susan", "DAVID"$]->$ output : $["$david$"]$

$//$ if one name like david exists more than one but in different shape like "David" or "DAVID" it should be counted and return all small letter $["$david$"]$

ex$3$ : $["$Alex$",$ "vansh","joe","Alex"$]->$ output : $["$alex$"]$

$//$ hint in the output array we do not have any capital letter, in case Alex exits $3$ times it should be returned in small for like $["$alex$"]$