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let any point D have been taken on the other side of the straight line AB,
and, with center C and distance CD,
let the circle EFG have been described, [Post.3]
and
let the straignt line EG have been bisected at H, [I.10]
and
let the straight lines CG, CH, CE have been joined. [Post.1]
I say that
CH has been drawn perpendicular to the given infinite straight line AB from the given point C which is not on it.
