VISIT consume_args.lean
SYNC 7
import logic data.nat.basic
open nat eq.ops

theorem tst (a b c : nat) : a + b + c = a + c + b :=
calc a + b + c = a + (b + c) : !add.assoc
         ...   = a + (c + b) : {!add.comm}
         ...   = a + c + b   : (!add.assoc)⁻¹
WAIT
INFO 7