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    Date: 3 August 1981 01:20-EDT
    From: Kent M. Pitman <KMP at MIT-MC>

    I suspect that few people make use of nary QUOTIENT and that those who do 
    could write (QUOTIENT A (quotient b ...)) themselves or a macro that expands
    into same. The same for DIFFERENCE. What if only the commutative math ops
    were allowed to be nary?

The key characteristic is associativity, not communtativity.
If we let * represent some non-commutative operation (such as matrix
multiplication), then (* A B C) makes perfect sense and is different
from (* A C B).

I don't use n-ary quotient, but I do use unary quotient as reciprocal.