Murray's work comes from the desire to represent mathematical equations
faithfully, based nearly entirely on the semantics of the operators and
having those operators be represented as Unicode characters.
One solution that he uses is the use of "redundant" parens. Parens can
be supplied to group operands, so that you get the correct precedence,
but, where they are not necessary to the human reader, they will be
dropped in the formatted equation.
As input format, the linear format, therefore looks more like current
source code, in that one does type parens.
When fractions are built up, you don't need the parens, so they are
dropped in layout. If you take the same fraction and display it inline
(with a slash) some or all of the parens would be needed for the human
reader as well, so those are displayed.
How would you parse 5.5 if input as a fraction? 51/2? You do need some
form of grouping to recognize that the 5 and the 1 are not part of the
same numerator.
A./
