Ballantine & Jerbert 1952 do not mention this restriction in their article Ballantine, J.P.; Jerbert, A.R. (1952), "Distance from a line or plane to a point", American Mathematical Monthly, 59 (4): 242–243, doi:10.2307/2306514, JSTOR2306514
Ballantine & Jerbert 1952 do not mention this restriction in their article Ballantine, J.P.; Jerbert, A.R. (1952), "Distance from a line or plane to a point", American Mathematical Monthly, 59 (4): 242–243, doi:10.2307/2306514, JSTOR2306514