set_option structureDiamondWarning false

class Foo (α : Type) extends Add α where
  zero : α

class FooComm (α : Type) extends Foo α where
  comm (a b : α) : a + b = b + a

class FooAssoc (α : Type) extends Foo α, Mul α where
  add_assoc (a b c : α) : (a + b) + c = a + (b + c)
  mul_assoc (a b c : α) : (a * b) * c = a * (b * c)

class FooAC (α : Type) extends FooComm α, FooAssoc α where
  mul_comm (a b : α) : a * b = b * a

set_option pp.all true
#check @FooAC.mk

#print FooAC.toFooAssoc

class FooAssoc' (α : Type) extends FooAssoc α where
  one : α

class FooAC' (α : Type) extends FooComm α, FooAssoc' α where
  mul_comm (a b : α) : a * b = b * a

#check @FooAC'.mk

#print FooAC'.toFooAssoc'

def f [FooAssoc α] (a : α) : α :=
  a * a

def g [FooAC' α] (a : α) : α :=
  f (a + FooAssoc'.one)