While the lake is the largest man-made lake around, some say it is not the state's largest lake, because some of it is in Ohio. The dam that formed the lake on the Shenango River was completed in 1934. The largest man-made lake built by the Army Corps of Engineers in Pennsylvania is Raystown Lake.
postulate (plural postulates) 1  Something assumed without proof as being self-evident or generally accepted, especially when used as a basis for an argument. 2  A fundamental element; a basic principle. ( 3 logic) An axiom. 4  A requirement; a prerequisite.
The parallel postulate. The fifth postulate in Euclid's Elements can be rephrased as. The postulate is not true in 3D, but in 2D it seems to be a valid statement. Considering the importance of postulates however, a seemingly valid statement is not good enough. Exactly one line through the red point is parallel to the thick white line.