composer.json

{
    "name": "clement/test",
    "description": "test",
    "require": {
        "silex/silex": "dev-master",
        "symfony/form": "dev-master",
        "twig/twig": "dev-master",
        "fp/lightopenid": "dev-master"

    },
    "authors": [
        {
            "name": "Clement JOBEILI",
            "email": "clement@yurplan.com"
        }
    ]
}

console

php composer.phar install
Installing dependencies


                                                                                                                                                                                                                                                                                                                               
  [Composer\DependencyResolver\SolverProblemsException]                                                                                                                                                                                                                                                                        
  [Job(cmd=install, target=symfony/form, packages=[symfony/symfony-9999999-dev, symfony/symfony-2.1.9999999.9999999-dev (alias of 9999999-dev), symfony/form-9999999-dev]), Job(cmd=install, target=twig/twig, packages=[twig/twig-9999999-dev]), Job(cmd=install, target=silex/silex, packages=[silex/silex-9999999-dev]), ]