diff --git a/go/lib/is/is.go b/go/lib/is/is.go
index 44dd64a32..a80df0590 100644
--- a/go/lib/is/is.go
+++ b/go/lib/is/is.go
@@ -1,11 +1,11 @@
-package common
+package is
 
 import (
 	"math/big"
 	"unicode"
 )
 
-func IsDigit(s string) bool {
+func Digit(s string) bool {
 	for _, r := range s {
 		if !unicode.IsDigit(r) {
 			return false
@@ -14,7 +14,7 @@ func IsDigit(s string) bool {
 	return true
 }
 
-func IsLower(s string) bool {
+func Lower(s string) bool {
 	for _, r := range s {
 		if !unicode.IsLower(r) {
 			return false
@@ -23,7 +23,7 @@ func IsLower(s string) bool {
 	return true
 }
 
-func IsUpper(s string) bool {
+func Upper(s string) bool {
 	for _, r := range s {
 		if !(r >= 'A' && r <= 'Z') {
 			return false
@@ -32,6 +32,6 @@ func IsUpper(s string) bool {
 	return true
 }
 
-func IsPrime(i int) bool {
+func Prime(i int) bool {
 	return big.NewInt(int64(i)).ProbablyPrime(0)
 }
diff --git a/go/tests/any/main.go b/go/tests/any/main.go
index 18f0ef983..7cfbd5a71 100644
--- a/go/tests/any/main.go
+++ b/go/tests/any/main.go
@@ -1,9 +1,9 @@
 package main
 
 import (
-	"../common"
 	"./student"
 	"github.com/01-edu/public/go/lib"
+	"github.com/01-edu/public/go/lib/is"
 )
 
 func any(f func(string) bool, arr []string) bool {
@@ -17,7 +17,7 @@ func any(f func(string) bool, arr []string) bool {
 }
 
 func main() {
-	functions := []func(string) bool{common.IsDigit, common.IsLower, common.IsUpper}
+	functions := []func(string) bool{is.Digit, is.Lower, is.Upper}
 
 	type node struct {
 		f func(string) bool
@@ -35,31 +35,31 @@ func main() {
 	}
 	for i := 0; i < 5; i++ {
 		table = append(table, node{
-			f: common.IsDigit,
+			f: is.Digit,
 			a: lib.MultRandDigit(),
 		})
 	}
 
 	for i := 0; i < 5; i++ {
 		table = append(table, node{
-			f: common.IsLower,
+			f: is.Lower,
 			a: lib.MultRandLower(),
 		})
 	}
 	for i := 0; i < 5; i++ {
 		table = append(table, node{
-			f: common.IsUpper,
+			f: is.Upper,
 			a: lib.MultRandUpper(),
 		})
 	}
 
 	table = append(table,
 		node{
-			f: common.IsDigit,
+			f: is.Digit,
 			a: []string{"Hello", "how", "are", "you"},
 		},
 		node{
-			f: common.IsDigit,
+			f: is.Digit,
 			a: []string{"This", "is", "4", "you"},
 		},
 	)
diff --git a/go/tests/countif/main.go b/go/tests/countif/main.go
index 8017fe252..6e1a2bded 100644
--- a/go/tests/countif/main.go
+++ b/go/tests/countif/main.go
@@ -1,9 +1,9 @@
 package main
 
 import (
-	"../common"
 	"./student"
 	"github.com/01-edu/public/go/lib"
+	"github.com/01-edu/public/go/lib/is"
 )
 
 func countIf(f func(string) bool, arr []string) int {
@@ -18,7 +18,7 @@ func countIf(f func(string) bool, arr []string) int {
 }
 
 func main() {
-	functions := []func(string) bool{common.IsDigit, common.IsLower, common.IsUpper}
+	functions := []func(string) bool{is.Digit, is.Lower, is.Upper}
 
 	type node struct {
 		f   func(string) bool
@@ -37,7 +37,7 @@ func main() {
 	}
 	for i := 0; i < 5; i++ {
 		val := node{
-			f:   common.IsDigit,
+			f:   is.Digit,
 			arr: lib.MultRandDigit(),
 		}
 		table = append(table, val)
@@ -45,14 +45,14 @@ func main() {
 
 	for i := 0; i < 5; i++ {
 		val := node{
-			f:   common.IsLower,
+			f:   is.Lower,
 			arr: lib.MultRandLower(),
 		}
 		table = append(table, val)
 	}
 	for i := 0; i < 5; i++ {
 		val := node{
-			f:   common.IsUpper,
+			f:   is.Upper,
 			arr: lib.MultRandUpper(),
 		}
 		table = append(table, val)
@@ -60,11 +60,11 @@ func main() {
 
 	table = append(table,
 		node{
-			f:   common.IsDigit,
+			f:   is.Digit,
 			arr: []string{"Hello", "how", "are", "you"},
 		},
 		node{
-			f:   common.IsDigit,
+			f:   is.Digit,
 			arr: []string{"This", "is", "4", "you"},
 		},
 	)
diff --git a/go/tests/findnextprime/main.go b/go/tests/findnextprime/main.go
index 31bcf72d0..dfc4a295d 100644
--- a/go/tests/findnextprime/main.go
+++ b/go/tests/findnextprime/main.go
@@ -1,13 +1,13 @@
 package main
 
 import (
-	"../common"
 	"./student"
 	"github.com/01-edu/public/go/lib"
+	"github.com/01-edu/public/go/lib/is"
 )
 
 func findNextPrime(nb int) int {
-	if common.IsPrime(nb) {
+	if is.Prime(nb) {
 		return nb
 	}
 	return findNextPrime(nb + 1)
diff --git a/go/tests/findprevprime/main.go b/go/tests/findprevprime/main.go
index 58404d79c..d1977323b 100644
--- a/go/tests/findprevprime/main.go
+++ b/go/tests/findprevprime/main.go
@@ -1,16 +1,16 @@
 package main
 
 import (
-	"../common"
 	"./student"
 	"github.com/01-edu/public/go/lib"
+	"github.com/01-edu/public/go/lib/is"
 )
 
 func findPrevPrime(nb int) int {
 	if nb < 2 {
 		return 0
 	}
-	if common.IsPrime(nb) {
+	if is.Prime(nb) {
 		return nb
 	}
 	return findPrevPrime(nb - 1)
diff --git a/go/tests/islower/main.go b/go/tests/islower/main.go
index 4af520b9c..46e3519b4 100644
--- a/go/tests/islower/main.go
+++ b/go/tests/islower/main.go
@@ -1,9 +1,9 @@
 package main
 
 import (
-	"../common"
 	"./student"
 	"github.com/01-edu/public/go/lib"
+	"github.com/01-edu/public/go/lib/is"
 )
 
 func main() {
@@ -39,6 +39,6 @@ func main() {
 		"hello!",
 	)
 	for _, arg := range table {
-		lib.Challenge("IsLower", student.IsLower, common.IsLower, arg)
+		lib.Challenge("IsLower", student.IsLower, is.Lower, arg)
 	}
 }
diff --git a/go/tests/isnumeric/main.go b/go/tests/isnumeric/main.go
index 3d3b43280..7cec8382e 100644
--- a/go/tests/isnumeric/main.go
+++ b/go/tests/isnumeric/main.go
@@ -3,9 +3,9 @@ package main
 import (
 	"strconv"
 
-	"../common"
 	"./student"
 	"github.com/01-edu/public/go/lib"
+	"github.com/01-edu/public/go/lib/is"
 )
 
 func main() {
@@ -33,6 +33,6 @@ func main() {
 		"01,02,03",
 	)
 	for _, arg := range table {
-		lib.Challenge("IsNumeric", student.IsNumeric, common.IsDigit, arg)
+		lib.Challenge("IsNumeric", student.IsNumeric, is.Digit, arg)
 	}
 }
diff --git a/go/tests/isprime/main.go b/go/tests/isprime/main.go
index 159d05da2..f14c2c3dd 100644
--- a/go/tests/isprime/main.go
+++ b/go/tests/isprime/main.go
@@ -1,9 +1,9 @@
 package main
 
 import (
-	"../common"
 	"./student"
 	"github.com/01-edu/public/go/lib"
+	"github.com/01-edu/public/go/lib/is"
 )
 
 func main() {
@@ -27,6 +27,6 @@ func main() {
 		1000000087,
 	)
 	for _, arg := range table {
-		lib.Challenge("IsPrime", student.IsPrime, common.IsPrime, arg)
+		lib.Challenge("IsPrime", student.IsPrime, is.Prime, arg)
 	}
 }
diff --git a/go/tests/isupper/main.go b/go/tests/isupper/main.go
index 01bf963a1..7cb29942b 100644
--- a/go/tests/isupper/main.go
+++ b/go/tests/isupper/main.go
@@ -1,9 +1,9 @@
 package main
 
 import (
-	"../common"
 	"./student"
 	"github.com/01-edu/public/go/lib"
+	"github.com/01-edu/public/go/lib/is"
 )
 
 func main() {
@@ -41,6 +41,6 @@ func main() {
 		"HELLO!",
 	)
 	for _, arg := range table {
-		lib.Challenge("IsUpper", student.IsUpper, common.IsUpper, arg)
+		lib.Challenge("IsUpper", student.IsUpper, is.Upper, arg)
 	}
 }
diff --git a/go/tests/map/main.go b/go/tests/map/main.go
index 758f74e14..444da880a 100644
--- a/go/tests/map/main.go
+++ b/go/tests/map/main.go
@@ -1,9 +1,9 @@
 package main
 
 import (
-	"../common"
 	"./student"
 	"github.com/01-edu/public/go/lib"
+	"github.com/01-edu/public/go/lib/is"
 )
 
 func isPositive(i int) bool {
@@ -25,7 +25,7 @@ func _map(f func(int) bool, a []int) []bool {
 }
 
 func main() {
-	functions := []func(int) bool{isPositive, isNegative0, common.IsPrime}
+	functions := []func(int) bool{isPositive, isNegative0, is.Prime}
 
 	type node struct {
 		f   func(int) bool
@@ -44,7 +44,7 @@ func main() {
 	}
 
 	table = append(table, node{
-		f:   common.IsPrime,
+		f:   is.Prime,
 		arr: []int{1, 2, 3, 4, 5, 6},
 	})