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ACROSS

 1 Something that can stop a car: a bikini during spring break, perhaps? (4,4)

 5 Legal participant in California’s capital, interrupting: “Am I American?” (6)

10 Former spouse criticizes particle growth (9)

11 Singable excerpt from Joely Richardson (5)

12 Murder victim is qualified to be heard (4)

13 Violinist playing 21 (5,5)

15 Ultimately, software bug limits overturning four-dimensional reality (5-4)

18 Jumping bail, I could produce a defense (5)

19 Military trainee acted without discipline (5)

20 Authoritarian jerk following notes—yes, you read that correctly—backward (9)

21 Discovers unlucky 13 (10)

23 Look over slide on mountain face (4)

26 Paint romantic setting for prologue (5)

27 Ball of wax tangled lead chain (9)

28 Clothes-free enthusiast swallows insult (6)

29 Discharged grass outside pastures (8)

DOWN

 1 Fornicates (offers the ingredients needed for uncensored writing) (4,11)

 2 Computer company’s program topping the French (5)

 3 Receptacle smelled nasty with the lid removed (4)

 4 Mars moves quickly around center of Jupiter (5)

 6 Trumpeter deceptively misleads (takes in) a couple of virtuosos (5,5)

 7 Worry cruelly tries someone determined to get ahead at all costs (9)

 8 Vice president incorporates bits from comedians, some of them repeatedly (6-2-7)

 9 Behaves scornfully about last pair of Slovak shoes (8)

14 Roman officers reinterpret runic notes (10)

16 Stepped down to thwart a bad edict (9)

17 Find unusual wrapper for unusual kind of radiation (8)

22 Hogshead hidden in pleasant compartment (5)

24 Poet takes in under $1,000 (5)

25 Long tree (4)

SOLUTION TO PUZZLE NO. 3299

ACROSS 1 BI(L + L + BOA)RD  6 anag. 9 DEB + ONE-D 10 anag.  11 anag. 12 PIG + EON (anag.)  14 AT(LANTI)C (act anag., Latin anag.) 17 “thyme” 20 rev. 21 anag.  23 [c]U(PDA)TE 24 anag. 28 G[ir]L + AMOUR 29 O(PALIN)E 30 D[o]WELL 31 MAGAZIN (anag.) + ES

DOWN 1 BO(D)Y 2 hidden  3 anag. 4 [p]ADDLE 5 DID + O  6 WIT + HIT 7 anag. 8 anag. 13 anag.  15 THIRD(RAT)E (dither anag.)  16 3 defs. 18 ASSUAGE (anag.) + D  19 CO(OLJ + AZ)Z (J.Lo rev.)  22 S + TROLL 24 A + MON + G  25 RE[s]IGN 26 G + RAM 27 rev.