什么是“ channel1 <-<-channel2”？

In Concurrency Go Patterns (https://www.youtube.com/watch?v=f6kdp27TYZs) there is an example of code that looks like:

func fanIn(in1 <-chan string) <-chan string {
    c:=make(chan string)
    go func() { 
        for {
            c <- <-in1 
        } 
    }() 
    return c
}

For me this looks very strange c <- <-in1. What does it mean?

The c <- <-in1 stands for:

in1Val := <-in1 // read from channel in1
c <- in1Val // write the value from in1 channel to `c` channel

If you write such kind of code first time - use more this detailed code to understand what happens better.