s into which they divide it and one of the diagonals of ABCD are concurrent.
Dem.—Let EH, GF meet in M; through M draw MP, MJ parallel to AB, BC. Produce AD, GH, BC to meet MP, and AB, EF, DC to meet MJ. Now the complement OF = FJ: to each add the
FL, and we get the figure OFL =
CJ. Again, the complement PH = HK [xliii.]: to each add the
OC, and we get the
PC = figure OFL. Hence the