Having two opposite faces plane and parallel a plane-parallel sheet of glass.
Or ?? ⬇️
In geometry, parallel lines are lines in a plane which do not meet; that is, two straight lines in a plane that do not intersect at any point are said to be parallel. Colloquially, curves that do not touch each other or intersect and keep a fixed minimum distance are said to be parallel.
The best deal would be "three for the price of two" since buying one and 25 percent off would be 17.5 plus 10 for a third one is 27.5 compared to 20 for 3
