Algebraic Entry Tutorial Exercise 3
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The result from `1 RET 0 /' will be the formula `1 / 0'.  The
"function" `/' cannot be evaluated when its second argument is zero,
so it is left in symbolic form.  When you now type `0 *', the result
will be zero because Calc uses the general rule that "zero times
anything is zero."

The `m i' command enables an "infinite mode" in which `1 / 0' results
in a special symbol that represents "infinity."  If you multiply
infinity by zero, Calc uses another special new symbol to show that
the answer is "indeterminate."  See Infinities, for further
discussion of infinite and indeterminate values.