Conflict between package requirements when updating to Drupal 8.4 When running composer update, I get the following error:

Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - Can only install one of: symfony/yaml[3.2.x-dev, 2.8.x-dev].
    - Can only install one of: symfony/yaml[v2.8.0, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.0-BETA1, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.1, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.10, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.11, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.12, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.13, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.14, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.15, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.16, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.17, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.18, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.19, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.2, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.20, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.21, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.22, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.23, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.24, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.25, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.26, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.27, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.28, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.3, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.4, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.5, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.6, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.7, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.8, 3.2.x-dev].
    - Can only install one of: symfony/yaml[v2.8.9, 3.2.x-dev].
    - Can only install one of: symfony/yaml[3.2.x-dev, v2.8.28].
    - drupal/core 8.4.0 requires symfony/yaml ~3.2.8 -&gt; satisfiable by symfony/yaml[3.2.x-dev].
    - Installation request for drupal/core 8.4.0 -&gt; satisfiable by drupal/core[8.4.0].
    - Installation request for symfony/yaml ~2.8 -&gt; satisfiable by symfony/yaml[2.8.x-dev, v2.8.0, v2.8.0-BETA1, v2.8.1, v2.8.10, v2.8.11, v2.8.12, v2.8.13, v2.8.14, v2.8.15, v2.8.16, v2.8.17, v2.8.18, v2.8.19, v2.8.2, v2.8.20, v2.8.21, v2.8.22, v2.8.23, v2.8.24, v2.8.25, v2.8.26, v2.8.27, v2.8.28, v2.8.3, v2.8.4, v2.8.5, v2.8.6, v2.8.7, v2.8.8, v2.8.9].


I've seen a few explanations for similar errors, but I can't figure out how to fix it. I assume it has something to do with incompatibilities between yaml versions. How do I go about solving this?
So, I've found a solution. I had to go into my composer.json file and specific these versions under require:

"drupal/core": "~8.4",
"drush/drush": "~9.0",


Once I updated those lines, I deleted the composer.lock file as well as the vendor directory. After that, I was able to install Drupal 8.4 using composer update --with-dependencies.