fun foo(
    a: Int, s: String = """c$a
    :${a + 1}d"""
): String {
    val x = """_${s}_"""
    val y = "_$a:${a + 1}d_"
    val z = """_c$a:${a + 1}d_"""
    val u = "_c$a\n:${a + 1}d_"
    return """ab${s}ef"""
}