 The propagator for this theory for a string starting at the endpoints formula_18 and ending at the endpoints formula_19 is a conformal function of the 4-dimensional invariant.A string field in endpoint-string theory is a function over the endpoints.Although it is natural to generalize the Poincaré transformations in order to find hidden symmetries in physics and thus narrow down the number of possible theories of high-energy physics, it is difficult to experimentally examine this symmetry as it is not possible to transform an object under this symmetry.