Proof that a lazy sequence is a stream and is only iterated once even with two filters

Sequence.swift

var sequencePoint: Int32 = 0
func printSequencePoint(context: String) {
    print("\(context): \(OSAtomicIncrement32(&sequencePoint))")
}

var g = (0..<10).generate()
let seq = lazy(AnySequence(anyGenerator { _ -> Int? in
    printSequencePoint("generator")
    return g.next()
    }))
    .filter { printSequencePoint("filter #1"); return $0 != 2 }
    .filter { printSequencePoint("filter #2"); return $0 != 4 }

for x in seq {
    printSequencePoint("loop")
    print("item: \(x)")
}

zResult.txt

generator: 1
filter #1: 2
filter #2: 3
loop: 4
item: 0
generator: 5
filter #1: 6
filter #2: 7
loop: 8
item: 1
generator: 9
filter #1: 10
generator: 11
filter #1: 12
filter #2: 13
loop: 14
item: 3
generator: 15
filter #1: 16
filter #2: 17
generator: 18
filter #1: 19
filter #2: 20
loop: 21
item: 5
generator: 22
filter #1: 23
filter #2: 24
loop: 25
item: 6
generator: 26
filter #1: 27
filter #2: 28
loop: 29
item: 7
generator: 30
filter #1: 31
filter #2: 32
loop: 33
item: 8
generator: 34
filter #1: 35
filter #2: 36
loop: 37
item: 9
generator: 38
Program ended with exit code: 0