https://kotlinlang.org/api/core/1.5/kotlin-stdlib/kotlin.collections/-abstract-mutable-set/retain-all.html
retainAll
retainall
https://kotlinlang.org/api/core/1.3/kotlin-stdlib/kotlin.collections/-abstract-mutable-set/retain-all.html
retainAll
retainall
https://www.w3schools.com/Java/ref_linkedlist_retainall.asp
Java LinkedList retainAll() Method
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java linkedlistretainallmethod