Hitoshi Hombu "Die Projektive Theorie der “paths” $3$-ter Ordnung $x^{\left( 3 \right)i} + H^i \left( {x,x^{\left( 1 \right)} ,x^{\left( 2 \right)} } \right) = 0$," Proceedings of the Imperial Academy, Proc. Imp. Acad. 14(2), 36-40, (1938)