allowed variable names in functions?

["A B" <gentosaker@xxxxxxxxx>]

Hello.
I suspect that in a  plpgsql function

DECLARE
c2 REAL;
cadiv REAL;

works but

c2 REAL;
c2div REAL;

doesn't.

Is this true, and if so, what are the rules for the names in the
function? I use 8.1.