adding empty map and its axiom
adding empty map and its axiom

YaccConstructor/FStar,A-Manning/FStar,hoheinzollern/FStar,MallabaevAzamat/FStar,hoheinzollern/FStar,A-Manning/FStar,aa755/FStar,msprotz/FStar,MallabaevAzamat/FStar,MallabaevAzamat/FStar,hoheinzollern/FStar,msprotz/FStar,msprotz/FStar,YaccConstructor/FStar,MallabaevAzamat/FStar,hoheinzollern/FStar,A-Manning/FStar,FStarLang/FStar,YaccConstructor/FStar,aa755/FStar,msprotz/FStar,aa755/FStar,YaccConstructor/FStar,aa755/FStar,FStarLang/FStar,FStarLang/FStar