For Module can't be instance , so can't call it directily , include it to class , new the class and call module.
module M1
module M2
class C3
def two
p 'this is two'
end
end
def one
p 'this is one'
end
end
end
class C1
include M1
include M1::M2
end
class C2
include C1::M2
end
C1::C3.new.two
C1.new.one
C2.new.one
#result
#"this is two"
#"this is one"
#"this is one"