how to reference a YAML “setting” from elsewhere in the same YAML file?

I have the following YAML:

paths:
  patha: /path/to/root/a
  pathb: /path/to/root/b
  pathc: /path/to/root/c

How can I “normalise” this, by removing /path/to/root/ from the three paths, and have it as its own setting, something like:

paths:
  root: /path/to/root/
  patha: *root* + a
  pathb: *root* + b
  pathc: *root* + c

Obviously that’s invalid, I just made it up. What’s the real syntax? Can it be done?