Variables cannot be redefined (no new variables on left side of :=)

---

examples/redefine-variable-fail/redefine_variable_fail.go

package main

import (
    "fmt"
)

func main() {
    a := 42
    fmt.Println(a)

    a := 13
    fmt.Println(a)

}

# command-line-arguments
./redefine_variable_fail.go:11:4: no new variables on left side of :=