  The free scalar field is studied on the Y-junction of three semi infinite
axes which is the simplest example of a non-manifold space. It is shown that
under an assumption that the junction point can not gain a macroscopic amount
of energy and charge the transmission rules for this system uniquely follow
from conservation of energy and charge. This result is also obtained in the
discrete version of the model. Some alternative approaches to the problem based
on quantum mechanics of Hamiltonian systems with constrains are discussed.
