[metapost] outputtemplate

[Birch]

I have incorporated the outputtemplate command in some metapost source files.
I am missing something.

The combination: "%j-or.%c.mps" is evaluated as a numeric equation or constant
equated to a string internal variable and generates an error.

I have to remove the outputtemplate command and rename the default to .mps on
the command line to use the eps in pdflatex.

Please tell me how to make mpost operate on the internal variable rather than
evaluating the expression %j - %c (or is it %j * %c).

-- Boris