Moreoever, a T program may halt in other ways, e.g. by running all its commands. Were it not for these facts, making a table for a program would infallibly tell us whether it halted. We will prove this in the second hand-out . Second, tables can help guarantee consistency. If one has only two columns, and only one action and one command call in each cell of the table, then the program cannot be inconsistent.
Programmers can use both methods to force a canonical halt.
This is the only way to communicate input to the program and machine. We cannot prevent this by arranging always to work from the right end of the tape, for then we might run out of tape on the right side. Both decisions are optional and may be changed to suit different purposes. If the order of the inputs matters to the function, then they are to be placed in order from left to right. When a program takes no input, or takes zero as its input, we will assume that that the program begins at any point on the tape sufficiently far from either end to permit the completion of the program without running out of tape.