In libraries, the package need not be called main nor do you need the main function. As libraries aren’t applications, you cannot build a binary file with them and you need the main package that is going to use them.

package arithmetic 
 
func Sum(args ...int) (res int) { 
    for _, v := range args { 
        res += v 
    } 
    return 
} 
package main 
 
import ( 
"fmt" 
 
"github.com/myName/libraries/arithmetic" 
) 
 
func main() { 
    sumRes := arithmetic.Sum(5, 6) 
    subRes := arithmetic.Subtract(10, 5) 
    multiplyRes := arithmetic.Multiply(8, 7) 
    divideRes, _ := arithmetic.Divide(10, 2) 
 
    fmt.Printf("5+6 is %d. 10-5 is %d, 8*7 is %d and 10/2 is %f\n", sumRes, subRes, multiplyRes, divideRes) 
}