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Query about definition of COMMON data type
A strict reading of the last two paragraphs on page 28 of the Mary Poppins
edition says that STRING is not a subtype of COMMON. This is because STRING
is (ARRAY STRING-CHAR 1), and STRING-CHAR is neither T nor a subtype of
COMMON. STANDARD-CHAR is a subtype of COMMON, but STRING-CHAR is not, and
is not necessarily a subtype of STANDARD-CHAR.
I assume this was not intentional, and STRING should be a subtype of
COMMON for the same reason that (ARRAY T) is a subtype of COMMON. I agree
that STRING-CHAR should not be a subtype of COMMON; that makes sense.