[PRL] symbology question

[Dave Herman]

What would be a good mathematical symbol for representing a relation 
between types that is neither symmetrically nor transitively closed? 
Specifically, it represents a relation whose interpretation is "T may be 
cast to U under a conversion".

I originally was using #\u2272 ("LESS-THAN OR EQUIVALENT TO") -- see

     http://www.alanwood.net/unicode/mathematical_operators.html

I liked the squiggly for suggesting "T and U are sort of the same", but 
I'm afraid the "less-than" connection suggests transitivity. I'm 
intrigued by:

     #\u22B0 ("PRECEDES UNDER RELATION")

but it may suffer the same problem -- "precedes" probably implies 
transitivity. I could use some sort of squiggly or curly arrow, but then 
it starts to look more like a reduction relation.

Thanks,
Dave "Johan Ovlinger" Herman