The Presentation of the Quantum Algebra of Observables of the Closed   Bosonic String in 1+3 Dimensions: The Presentation in Manifestly Lorentz   Covariant Form
  The quantum algebra of observables of the massive closed bosonic string in 1+3 dimensions has been developed so far in the rest frame of the string. In this paper a method to write this algebra in a manifestly Lorentz covariant form is explained and compared with an alternative approach in the literature. 
Diethard Peter