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The difficulty is that as defined, < is not an order 
relation, because there exist values a, b, c such that a<b, 
b==c, and a==c.  I believe that there also exist values 
such that a<b, b<c, and a==c.  Under such circumstances, it 
is hard to understand how sort can work properly, whicn is 
my real concern.  Do you really want to warn people that 
they shouldn't sort lists containing floats and longs?

Moreover, it is not terribly difficult to define the 
comparisons so that == is an equivalence relation and < is 
an order relation.  The idea is that for any floating-point 
system, there is a threshold T such that if x is a float 
value >=T, converting x to long will not lose information, 
and if x is a long value <=T, converting x to float will 
not lose information.  Therefore, instead of always 
converting to long, it suffices to convert in a direction 
chosen by comparing the operands to T (without conversion) 
first.