init()

What is the execution sequence of init() in the go files below.

// A/a1.go
package A
func init() {
    println("a1")
}
var A1 = ""
// A/a2.go
package A
func init() {
    println("a2")
}
var A2 = ""
// B/b1.go
package B
func init() {
    println("b1")
}
var B1 = ""
// B/b2.go
package B
import "github.com/test/A"
func init() {
    println("b2")
}
func f() {
    _ = A.A2
}
var B2 = ""
// C/main.go
package main
import (
    "github.com/test/B"
)
func main() {
    _ = B.B2
}
                        

Answer

a1
a2
b1
b2