Where is Assert defined

I tried to find which header file Assert is defined in but could not. Has it been removed? Or am I just blind or stupid and dont know how to use grep?

$ROOTSYS/lib/cint/include/assert.h

This one?

Note that to avoid confusion with other header and tools ‘Assert’ was renamed ‘R__ASSERT’ (in 5.14/00 and above)

Cheers,
Philippe