feat: make informal_definition and informal_lemma commands (#300)

* make informal_definition and informal_lemma commands
* drop the fields "math", "physics", and "proof" from InformalDefinition/InformalLemma and use docstrings instead
* render informal docstring in dependency graph

HepLean/BeyondTheStandardModel/TwoHDM/GaugeOrbits.lean

@@ -84,17 +84,19 @@ lemma prodMatrix_smooth (Φ1 Φ2 : HiggsField) :
     simpa only [prodMatrix, Fin.zero_eta, Fin.isValue, of_apply, cons_val', cons_val_zero,
       empty_val', cons_val_fin_one] using smooth_innerProd _ _
 
+/-- The map `prodMatrix` is invariant under the simultanous action of `gaugeAction` on the two Higgs
+fields. -/
 informal_lemma prodMatrix_invariant where
-  math :≈ "The map ``prodMatrix is invariant under the simultanous action of ``gaugeAction
-    on the two Higgs fields."
-  deps :≈ [``prodMatrix, ``gaugeAction]
+  deps := [``prodMatrix, ``gaugeAction]
 
+/-- Given any smooth map `f` from spacetime to 2-by-2 complex matrices landing on positive
+semi-definite matrices, there exist smooth Higgs fields `Φ1` and `Φ2` such that `f` is equal to
+`prodMatrix Φ1 Φ2`.
+
+See https://arxiv.org/pdf/hep-ph/0605184
+-/
 informal_lemma prodMatrix_to_higgsField where
-  math :≈ "Given any smooth map ``f from spacetime to 2 x 2 complex matrices landing on positive
-    semi-definite matrices, there exist smooth Higgs fields ``Φ1 and ``Φ2 such that
-    ``f is equal to ``prodMatrix Φ1 Φ2."
-  deps :≈ [``prodMatrix, ``HiggsField, ``prodMatrix_smooth]
-  ref :≈ "https://arxiv.org/pdf/hep-ph/0605184"
+  deps := [``prodMatrix, ``HiggsField, ``prodMatrix_smooth]
 
 end
 end TwoHDM