static S ai_html_renderTriple(WebRelation r) {
  ret r == null ? "" 
    : ai_html_encyclopediaTopic(r.a) + ai_html_triangle()
    + ai_html_encyclopediaTopic(r) + ai_html_triangle()
    + ai_html_encyclopediaTopic(r.b);
}

static S ai_html_renderTriple(T3<Symbol> t) {
  ret t == null ? "" 
    : ai_html_encyclopediaTopic(t.a) + ai_html_triangle()
    + ai_html_encyclopediaTopic(t.b) + ai_html_triangle()
    + ai_html_encyclopediaTopic(t.c);
}