{{ define "topics" }}
{{ $categoryCount := len .Papers.List }}
{{ if gt $categoryCount 0 }}
  <p>Topics: 
  {{ $first := true -}}
  {{- range $category, $paper := .Papers.List -}}
  {{- if $first -}}{{- $first = false -}}{{- else -}}, {{ end -}}
  <a href="#{{ $category }}">{{ $category }}</a>
  {{- end -}}.</p>
{{ else }}
  <p>nothing here yet.</p>
{{ end }}
{{ end }}