@gr36 IIRC, @sod solved this problem for @Mtt on the Help Forum

@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 }}