Forder writes on Fano's axiom in projective geometry on p. 305 of The Principles of Mathematics.

The letter has "193" before and after the street name, but this really seems to be Forder's house number. He taught school upon leaving Cambridge in 1910, and perhaps he did so at the school nearby 193 Windsor Rd., Oldham (which is in the Manchester area). The letter may be later than 1910 but no later than 1913, when he ceased teaching in Oldham. Forder states that he is "late of Sidney Coll" [Cambridge]. (He took both Parts of the Mathematics Tripos there.) BR did not note that he answered the letter. Forder writes at the end: "Permit me to conclude by thanking you for the great pleasure which your work has afforded me."

Forder notes in the brief Literature section of his The Foundations of Euclidean Geometry (CUP, 1927) that the logical background of any mathematical theory is discussed in Russell, IMP, Whitehead and Russell, PM (2nd Edition, 1925), Wittgenstein, TLP, Burali-Forti, Logica Matematica (2nd ed., 1919), and Peano, Formulario Mathematico (1908 and earlier eds.).