fix: lesson structure issue

frontend/src/utils/index.js

@@ -483,3 +483,19 @@ export function getLineStartPosition(string, position) {
 
 	return position
 }
+
+export function singularize(word) {
+    const endings = {
+        ves: 'fe',
+        ies: 'y',
+        i: 'us',
+        zes: 'ze',
+        ses: 's',
+        es: 'e',
+        s: ''
+    };
+    return word.replace(
+        new RegExp(`(${Object.keys(endings).join('|')})$`), 
+        r => endings[r]
+    );
+}