Fix: Prevent duplicate valid attendances

overlord/package.json

@@ -48,7 +48,6 @@
     "@angular/compiler-cli": "^12.2.4",
     "@angular/language-service": "^12.2.4",
     "@types/jasmine": "~3.7.4",
-    "@types/mathjs": "^9.4.2",
     "@types/node": "^16.7.10",
     "@typescript-eslint/eslint-plugin": "4.30.0",
     "@typescript-eslint/parser": "4.30.0",