The most basic rules in any programming language are those which govern the source form. These rules determine exactly how statements in a program are entered into the computer and how they are displayed. The source form rules are analogous to those fundamentals of natural language which define the alphabet used to express the words in the language, the punctuation symbols to be used, how sentences are to be written (left to right, up and down, right to left, etc.). These are the rules we are going to describe here.