Extend the set of default rewrites used by rewriting and simplification.
DESCRIPTION
The HOL Light rewriter (REWRITE_TAC etc.) and simplifier (SIMP_TAC etc.)
have default sets of (conditional) equations and other conversions that are
applied by default, except in the PURE_ variants. A call to
extend_basic_rewrites thl extends the former with the list of theorems thl,
so they will thereafter happen by default.