This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 110b. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
7.6.6 [expr.add] paragraph 8 explicitly allows subtraction of two pointers to functions:
If two pointers point to the same object or function... and the two pointers are subtracted...However, 7.6.6 [expr.add] paragraph 2 requires that two pointers that are subtracted be pointers to an object type; function pointers are not allowed.
Being able to subtract two pointers to functions doesn't seem terribly useful, especially considering that subtracting two pointers to different functions appears to produce undefined behavior rather than simply a non-zero result, according to paragraph 6:
Unless both pointers point to elements of the same array object, or one past the last element of the array object, the behavior is undefined.
Proposed resolution (10/00):
Remove the words or function from paragraph 8.