Radio Shack TRS-80 PC-3 Owner's Manual page 59

A function can be used any place that a variable can be used. Many functions do not require the use of parentheses.
LOG 100
is the same as
LOG (100)
You must use parentheses for functions which have more than one argument. Using parentheses always makes programs clearer.
See Chapter 8 for a complete Iist of functions available on the
PC-3.
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