  One of the key elements of Feynman's formulation of non-relativistic quantum
mechanics is a so-called Feynman path integral. It plays an important role in
the theory, but it appears as a postulate based on intuition rather than a
well-defined object. All previous attempts to supply Feynman's theory with
rigorous mathematics have not been satisfactory. The difficulty comes from a
need to define a measure on the infinite dimensional space of paths and to
create an integral that would possess all of the properties requested by
Feynman.
  In the present paper, we consider a new approach to defining the Feynman's
path integral, based on the theory developed by P. Muldowney. Muldowney uses
the Henstock integration technique, and non-absolute integrability of the
Fresnel integrals in order to obtain a representation of the Feynman's path
integral as a functional. This approach offers a mathematically rigorous
definition supporting Feynman's intuitive derivations. But in his work,
Muldowney gives only local in space-time solutions. A physical solution to the
non-relativistic Schr\"odinger equation must be global, and it must be given in
the form of a unitary one-parameter group in L^2. The purpose of this paper is
to show that one-dimensional Muldowney's local solutions may be extended to
yield a global solution. Moreover, the global extension can be represented by a
unitary one-parameter group acting in L^2.
