@gr36 Depending on your end goal, you could use a modified version of what’s in this conversation. Thanks to @sod for helping on that.
@gr36 That looks like you’re setting the variable to something then overwriting it. Are you trying to list all posts that have a Photo?
@gr36 Something like this may work. I typed it out on my phone and haven’t tested, so there may be a typo:
{{ if and (in .Params.categories "micro") (not (in Params.categories "photo")) }}
<h3>{{ .Title }}</h3>
{{ end }}
@gr36 One solution using complement: {{ range .Site.Taxonomies.categories.micro.Pages | complement .Site.Taxonomies.categories.photo.Pages }}.