Unicode-Symbole für DB+DD+SemWeb

  * <https://dbai.tuwien.ac.at/education/dm/resources/symbols.html>, einfach aus
    der "symbol"-Spalte kopieren

   σ π ρ ←
   ∪ ∩ 	  
   ✕ ÷ ⋈  ⋉  ⋊ 
   the outer joins have strange sizes (horizontal/vertical)  ⟕ ⟖ ⟗
   ∧ ∨ ¬ ≥ ≤ ≠  ≡ ∃ ∀

   ⊢ ⊨

   frog, penguin, dragon: 🐸  🐧 🐉
   Further unicode animals:
   <https://graphemica.com/characters/tags/animal>


   ← → ↔  ⇐ ⇒  ⇔
   ∑ ∈ ∉ ∋ ∌  ∞ ≠ ≤ ≥
   ∅ ⊆ ⊇ ⊈ ⊉ ⊊ ⊋ ∪ ⊍

   ω

   DL:  ≡ ⊑ ⊒ ⊓ ⊔ ⊤ ⊥ ∃ ∀