Subfields generated by a set (#4553)

* Subfields generated by a set

* Use sub-division-rings in the definition of generated subfields

* therefore > hence

* Shortened and renamed ~ recrng

* Update changes-set.txt

* Moved `fldsdrgfld` to main, comment updated.

* Rewrap

* fldcrng > fldcrngo

* Link to ~ fldsdrgfld in ~ df-sdrg

* Regen discouraged

* Editorial changes, and one shortening.

* Rewrap

* Update definition of sub-division-rings

changes-set.txt

@@ -87,6 +87,8 @@ make a github issue.)
 
 DONE:
 Date      Old       New         Notes
+11-Jan-25 fldcrng   fldcrngo
+11-Jan-25 recrng    resrng
 11-Jan-25 ---       ---         Moved surreal ordering theorems from
                                 SF's mathbox to main set.mm
 11-Jan-25 ---       ---         Moved ordinal sequence theorems from
@@ -95,6 +97,9 @@ Date      Old       New         Notes
 11-Jan-25 3orel13   [same]      Moved from SF's mathbox to main set.mm
 11-Jan-25 3pm3.2ni  [same]      Moved from SF's mathbox to main set.mm
 10-Jan-25 syl5bi    biimtrid
+10-Jan-25 fldcrngd  [same]      Moved from SN's mathbox to main set.mm
+10-Jan-25 drngringd [same]      Moved from SN's mathbox to main set.mm
+10-Jan-25 drnggrpd  [same]      Moved from SN's mathbox to main set.mm
  9-Jan-25 fvresval  [same]      Moved from SF's mathbox to main set.mm
  9-Jan-25 brtp      [same]      Moved from SF's mathbox to main set.mm
  9-Jan-25 ---       ---         Moved initial surreal definitions from

discouraged

@@ -4783,7 +4783,7 @@
 "df-erq" is used by "nqerid".
 "df-erq" is used by "nqerrel".
 "df-exid" is used by "isexid".
-"df-fld" is used by "fldcrng".
+"df-fld" is used by "fldcrngo".
 "df-fld" is used by "flddivrng".
 "df-fld" is used by "isfld2".
 "df-gcdOLD" is used by "ee7.2aOLD".
@@ -5563,7 +5563,7 @@
 "drnfc1" is used by "nfcvb".
 "drnfc1" is used by "nfriotad".
 "drngoi" is used by "dvrunz".
-"drngoi" is used by "fldcrng".
+"drngoi" is used by "fldcrngo".
 "drsb1" is used by "iotaeq".
 "drsb1" is used by "sb2ae".
 "drsb1" is used by "sbco3".