2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/203401We choose such boundary conditions for open IIB superstring theory which preserve N=1 SUSY. The explicite solution of the boundary conditions yields effective theory which is symmetric under world-sheet parity transformation $Ω:σ\to-σ$. We recognize effective theory as closed type I superstring theory. Its background fields,beside known $Ω$ even fields of the initial IIB theory, contain improvements quadratic in $Ω$ odd ones.4 revtex pages, no figuresHigh Energy Physics - Theorytext