show 𝓖.pathLabel (_ ++ _) = _
case mk.mk
V : Type u_1
E : Type u_2
G : Type u_3
Γ : Graph V E
inst✝ : Group G
u✝ v✝ w✝ : V
g h : G
𝓖 : GroupLabelledGraph Γ G
u v w : V
p : Graph.EdgePath Γ u v
p' : Graph.EdgePath Γ v w
⊢ pathClassLabel 𝓖 (Quot.mk Graph.EdgePath.Reduction p ≫ Quot.mk Graph.EdgePath.Reduction p') =
    pathClassLabel 𝓖 (Quot.mk Graph.EdgePath.Reduction p) * pathClassLabel 𝓖 (Quot.mk Graph.EdgePath.Reduction p')
case mk.mk
V : Type u_1
E : Type u_2
G : Type u_3
Γ : Graph V E
inst✝ : Group G
u✝ v✝ w✝ : V
g h : G
𝓖 : GroupLabelledGraph Γ G
u v w : V
p : Graph.EdgePath Γ u v
p' : Graph.EdgePath Γ v w
⊢ pathLabel 𝓖 (p ++ p') =
    pathClassLabel 𝓖 (Quot.mk Graph.EdgePath.Reduction p) * pathClassLabel 𝓖 (Quot.mk Graph.EdgePath.Reduction p')