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We prepared atomically clean Bi 2 Sr 2 CaCu 2 O 81d Josephson junctions between identical single crystal cleaves stacked and twisted an angle f 0 about the c axis. For each bicrystal, the ratio J J c ͞J S c of the c axis twist junction critical current density to that across either single crystal part is unity, independent of f 0 and the ratio A J ͞A S of junction areas. Our results provide strong evidence for incoherent caxis tunneling and that the dominant superconducting order parameter contains an isotropic s-wave component for T # T c , but not the purported d x 2 2y 2 -wave component.