Valid compinations of ESQL and Online?

I have a stupid question, but the answer is needed to make a precise decission. Which ESQL and 4GL versions are working with which Online versions? Or more specially, can I use an ESQL 7.1, development system with an Online 5.1 development engine to build up my application? If so, can I use the binary generated for installing and using it at our customer, who has an ESQL 7.1 runtime system and an Online 7.1 runtime engine? The problem is that we are develloping software for a customer, but we still have the older Online engine (5.1). Because we don't want to invest any mony for a new Online engine (7.1), just for the ESQL (7.1), we hope that this is possible. The same question holds on for the valid combinations of 4GL (4.1 and 6.x) and Online engine (5.1 and 7.1) Thanks for any comments, Chris P.S: I think that this is also an important and interesting information, so it also should be included in the FAQ?!