mathlib3

9ff74582 - feat(algebra/group_power/basic): add abs_add_eq_add_abs_iff (#6593)

feat(algebra/group_power/basic): add abs_add_eq_add_abs_iff (#6593) I've added ``` lemma abs_add_eq_add_abs_iff {α : Type*} [linear_ordered_add_comm_group α] (a b : α) : abs (a + b) = abs a + abs b ↔ (0 ≤ a ∧ 0 ≤ b ∨ a ≤ 0 ∧ b ≤ 0) ``` from `lean-liquid`. For some reasons I am not able to use `wlog hle : a ≤ b using [a b, b a]` at the beginning of the proof, Lean says `unknown identifier 'wlog'` and if I try to import `tactic.wlog` I have tons of errors.