#exit
inductive tree (A : Type) : Type :=
| node : A → forest A → tree A
with forest : Type :=
| nil  : forest A
| cons : tree A → forest A → forest A


#check tree.{1}
#check forest.{1}
#check tree.rec.{1 1}
#check forest.rec.{1 1}

#print "==============="

inductive group : Type :=
mk_group : Π (carrier : Type) (mul : carrier → carrier → carrier) (one : carrier), group

#check group.{1}
#check group.{2}
#check group.rec.{1 1}
