In Diophantine Equations (page 209), Mordell writes:
[Skolem] proved that the equation $$x^5+2y^5+4z^5-10xy^3z+10x^2yz^2=1$$ has at most six solutions in integers $x,y,z$, and of these three are known, namely $(x,y,z)=(1,0,0),(-1,1,0),(1,1,-2).$
Question #1: Does anyone know if progress has been made on solving this equation since Mordell wrote that (1969)? I’ve been looking, but haven’t found anything.
Question #2: Is there a translation of Skolem’s book/paper anywhere, in which this “Theorem 9” can be found?