Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires infection/infection ^0.29.0 -> satisfiable by infection/infection[0.29.0]. - maglnet/composer-require-checker 3.8.0 requires nikic/php-parser ^4.13.0 -> satisfiable by nikic/php-parser[v4.13.0, ..., v4.19.1]. - You can only install one version of a package, so only one of these can be installed: nikic/php-parser[v4.6.0, ..., v4.19.1, v5.0.0, v5.0.1, v5.0.2]. - infection/infection 0.29.0 requires nikic/php-parser ^5.0 -> satisfiable by nikic/php-parser[v5.0.0, v5.0.1, v5.0.2]. - Root composer.json requires maglnet/composer-require-checker ^3.8.0 -> satisfiable by maglnet/composer-require-checker[3.8.0]. Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.