[PHP4BETA]: require strategies

How do you folks deal with the following problem (if you ever do): FOO requires BAZ, and BAR requires BAZ, and FOO requires BAR. If both FOO and BAR include BAZ, then a function redefinition error occurs. If FOO is left responsible for including BAZ, and BAR is used independently of FOO (without being included by FOO) then FOO has not included BAZ, and an undefined function error occurs. It seems to me that require() should be responsible for tracking this kind of stuff, but it doesn't seem to be. Also, I though about writing a function to track repeated includes and not repeat, but including that function would subject to the same conundrum as above. Any ideas? -Daniel