Is there a function in Informix SQL that will return the position of a substring? I have tried INSTR(), POSITION(), AT()...

The manuals I have for Informix SQL give no indication as to the existence of such a function.

Here's an example of what I'm trying to do:

SELECT c.last_name,
at('-',c.last_name)
FROM client c
WHERE c.last_name LIKE '%-%'

Thanks in advance!!!
Susan