Symfony 3.1 composer conflicts - symfony

Question

I'm resuscitating the old Symfony project.
Cannot "composer install". I have tried to make changes in packages removing composer.lock , changing versions of packages. Bugs are multiplying.
Is there a way to resolve this conflict ?
Problem 1
- symfony/debug is locked to version dev-master and an update of this package was not requested.
- Only one of these can be installed: symfony/symfony[v3.1.0], symfony/debug[dev-master]. symfony/symfony replaces symfony/debug and thus cannot coexist with it.
- symfony/symfony is locked to version v3.1.0 and an update of this package was not requested.
composer.json :
{
"name": "symfony/framework-standard-edition",
"license": "MIT",
"type": "project",
"description": "The \"Symfony Standard Edition\" distribution",
"autoload": {
"psr-4": { "": "src/" },
"classmap": [ "app/AppKernel.php", "app/AppCache.php" ]
},
"autoload-dev": {
"psr-4": { "Tests\\": "tests/" }
},
"require": {
"php": ">=5.5.9",
"symfony/symfony": "3.1",
"twig/extensions": "^1.4",
"doctrine/orm": "^2.5",
"doctrine/doctrine-bundle": "^1.6",
"doctrine/doctrine-cache-bundle": "^1.2",
"doctrine/doctrine-migrations-bundle": "^1.2",
"symfony/swiftmailer-bundle": "^2.3",
"symfony/monolog-bundle": "^2.8",
"symfony/polyfill-apcu": "^1.0",
"symfony/debug": "3.2.x-dev",
"sensio/distribution-bundle": "^5.0",
"sensio/framework-extra-bundle": "^3.0.2",
"incenteev/composer-parameter-handler": "^2.0",
"liuggio/excelbundle": "^2.1",
"stof/doctrine-extensions-bundle": "1.2.*#dev",
"friendsofsymfony/user-bundle": "^2.0",
"friendsofsymfony/jsrouting-bundle": "^2.0",
"jms/serializer-bundle": "^1.1",
"yethee/enum-bundle": "^2.0",
"webit/eval-math": "^1.0",
"yavin/symfony-form-tree": "^1.0",
"knplabs/knp-snappy-bundle": "^1.4",
"friendsofsymfony/rest-bundle": "^2.1"
},
"require-dev": {
"sensio/generator-bundle": "^3.0",
"symfony/phpunit-bridge": "^3.0"
},
"scripts": {
"symfony-scripts": [
"Incenteev\\ParameterHandler\\ScriptHandler::buildParameters",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::buildBootstrap",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::clearCache",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installAssets",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installRequirementsFile",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::prepareDeploymentTarget"
],
"post-install-cmd": [
"#symfony-scripts"
],
"post-update-cmd": [
"#symfony-scripts"
]
},
"config": {
"bin-dir": "bin",
"platform": {
"php": "5.5.9"
}
},
"minimum-stability": "dev",
"extra": {
"symfony-app-dir": "app",
"symfony-bin-dir": "bin",
"symfony-var-dir": "var",
"symfony-web-dir": "web",
"symfony-tests-dir": "tests",
"symfony-assets-install": "relative",
"incenteev-parameters": {
"file": "app/config/parameters.yml"
},
"branch-alias": {
"dev-master": "3.2-dev"
}
}
}

Answer 1

I have no idea how this package version got there.
I was trying to pick the closest version number from packagist before
I have chosen the simplest approach to the problem this time :).
I have been downgrading it number by number to 3.1.0 when it finally ran.