code: public function isPackageInstalled(InstalledRepositoryInterface $repo, PackageInterface $package)
      {
          if ($package instanceof AliasPackage) {
              return $repo->hasPackage($package) && $this->isPackageInstalled($repo, $package->getAliasOf());
          }
  
          return $this->getInstaller($package->getType())->isInstalled($repo, $package);
      }
docs: Checks whether provided package is installed in one of the registered installers.
  
  @param InstalledRepositoryInterface $repo    repository in which to check
  @param PackageInterface             $package package instance
  
  @return bool