(Beginners should omit this section.)
Users may define their own new infix operators by specifying the precedence after the word `define'. E.g. to define an operation of precedence -3.5 /// which divides its first argument by the square of its second, and associates to the right:
    define -3.5 x /// y;
        x / (y * y)
    enddefine;
    3 /// 4 =>
    ** 0.1875
    4 /// 5 =>
    ** 0.16
    3 /// 4 /// 5 =>
    ** 117.187
    (3 /// 4) /// 5 =>
    ** 0.0075
Infix procedures are available for other purposes besides numerical
operations. We have already seen that "<>" is an infix operation which
can join two lists or two procedures together, for instance, and
"matches" is an infix operation used for comparing two lists.
    identprops("matches") =>
    ** 8
The equality symbols "=" and "==" are also used as infix operators
applicable to arbitrary objects.