Construct an equilateral triangle with one vertex on each of three parallel lines using just a straight edge and a pair of compasses.
Construct a line parallel to this with the same distance between them as the bottom two lines: find the point of intersection of this line with the bottom line, construct a circle through this point with centre on the original point, find the intersections of this circle with the bottom two lines and draw a line through these.
Find the intersection of this line with the top line and then draw a circle with a centre on the original point that passes through this point. Find the intersection of this circle with the bottom line (on the same side as the top point).