A spreadsheet consists of a table of "cells" arranged into rows and columns and referred to by the X and Y locations. X locations, the columns, are normally represented by letters, "A", "B", "C", etc., while rows are normally represented by numbers, 1, 2, 3, etc. A single cell can be referred to by addressing its row and column, "C10" for instance. This electronic concept of cell references was first introduced in LANPAR (Language for Programming Arrays at Random) (co-invented by Rene Pardo and Remy Landau) and a variant used in VisiCalc, and known as "A1 notation".