Cleaned up the engine interface a bit.  Experimenting with a way to reuse/refer to rules that makes the use apparent in the rule signature, see Eq.fsi, which is desirable both because this way the signature is more complete - you can better understand what Eq provides by reading the signature (fix rule is visible) - and also because this way the Eq rules object is more self-contained - you don't need to look at the engine invocation for additional rules.  Also experimenting a bit with the Rec proxy implementation.