A call to SRULE ths th simplifies the theorem th using the
standard simpset (accessible through a call to srw_ss()) and the
theorems ths, returning the simplified theorem.
The implementation of SRULE is
fun SRULE ths th = SIMP_RULE (srw_ss()) ths th
The fact that this definition is not eta-reduced means that partial
applications of SRULE will continue to pick up the current value of
srw_ss() when they are eventually fully applied, rather than bake in
the value from the time of the partial application.