From 7cd117dac1f440f04767a1502b5db2ce5232a45f Mon Sep 17 00:00:00 2001
From: Danila Fedorin <danila.fedorin@gmail.com>
Date: Sun, 10 Sep 2017 20:17:49 -0700
Subject: [PATCH] Add synchronization to the Standard plugin.

---
 core/src/main/java/org/nwapw/abacus/plugin/StandardPlugin.java | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/core/src/main/java/org/nwapw/abacus/plugin/StandardPlugin.java b/core/src/main/java/org/nwapw/abacus/plugin/StandardPlugin.java
index e144bbc..b3b16f0 100755
--- a/core/src/main/java/org/nwapw/abacus/plugin/StandardPlugin.java
+++ b/core/src/main/java/org/nwapw/abacus/plugin/StandardPlugin.java
@@ -696,8 +696,7 @@ public class StandardPlugin extends Plugin {
      * @param n              non-negative integer.
      * @return a number of numClass with value n factorial.
      */
-    public static NumberInterface factorial(NumberImplementation implementation, int n) {
-
+    synchronized public static NumberInterface factorial(NumberImplementation implementation, int n) {
         if (!FACTORIAL_LISTS.containsKey(implementation)) {
             FACTORIAL_LISTS.put(implementation, new ArrayList<>());
             FACTORIAL_LISTS.get(implementation).add(implementation.instanceForString("1"));