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## Starting and Terminating an Asir session

Run Asir, then the copyright notice and the first prompt will appear on your screen, and a new Asir session will be started.

    [0]

When initialization file ``$HOME/.asirrc'` exists, Asir interpreter executes it at first taking it as a program file written in Asir.

The prompt indicates the sequential number of your input commands to Asir. The session will terminate when you input `end;` or `quit;` to Asir. Input commands are evaluated statement by statement. A statement normally ends with its terminator ``;'` or ``$'`. (There are some exceptions. See, syntax of Asir.) The result will be displayed when the command, i.e. statement, is terminated by a ``;'`, and will not when terminated by a ``$'`.

    % asir
    [0] A;
    0
    [1] A=(x+y)^5;
    x^5+5*y*x^4+10*y^2*x^3+10*y^3*x^2+5*y^4*x+y^5
    [2] A;
    x^5+5*y*x^4+10*y^2*x^3+10*y^3*x^2+5*y^4*x+y^5
    [3] a=(x+y)^5;
    evalpv : invalid assignment
    return to toplevel
    [3] a;
    a
    [4] fctr(A);
    [[1,1],[x+y,5]]
    [5] quit;
    %

In the above example, names `A`, `a`, `x` and `y` are used to identify mathematical and programming objects. There, the name `A` denotes a program variable (some times called simply as a program variable.) while the other names, `a`, `x` and `y`, denote mathematical objects, that is, indeterminates. In general, program variables have names which begin with capital letters, while names of indeterminates begin with small letters. As you can see in the example, program variables are used to hold and keep objects, such as numbers and expressions, as their values, just like variables in C programming language. Whereas, indeterminates cannot have values so that assignment to indeterminates are illegal. If one wants to get a result by substituting a value for an indeterminate in an expression, it is achieved by the function `subst` as the value of the function.

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