vertexGroup — Mathlib

English

Same as above, specifying equality of arrows in the full D via their projections.

Русский

То же самое про стрелы в полной D через их проекции.

LaTeX

$$$f = g \\iff f.1 = g.1$$$

Lean4

/-- The vertex group at `c`. -/
@[simps mul one inv]
instance vertexGroup (c : C) : Group (c ⟶ c)
    where
  mul := fun x y : c ⟶ c => x ≫ y
  mul_assoc := Category.assoc
  one := 𝟙 c
  one_mul := Category.id_comp
  mul_one := Category.comp_id
  inv := Groupoid.inv
  inv_mul_cancel := inv_comp

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