`listOf(1,2).filter { a(it) }.map { b(it) }` Here ...
# stdlib
o
listOf(1,2).filter { a(it) }.map { b(it) }
Here we call a(1), a(2) and then b(1), b(2) If you fuse them, it would be a(1), b(1), a(2), b(2)