The occasion of this cryptic crossword was the workshop Satisfiability Lower Bounds and Tight Results for Parameterized and Exponential-Time Algorithms (Nov. 2 – Nov. 6, 2015, Simons Institute for the Theory of Computing, Berkeley, California, United States) that I had the pleasure of co-organising.

The grid is a bit more difficult than usual, with several entries less than 50% checked, and two 15-letter words. Some of the clues (and jokes) make little sense if you’re not the in target group of theoretical computer scientists.

Across

9 School on a graph isomorphism base. (9)
10 Who does the grading in Greek? (5)
11 Maybe a forest is better. (7)
12 Bizarre airlines ignoring N. Alon, say. (7)
13 Indian author of assumption about finding 14 across fast. (4)
14 Idiot workers take gin cocktail to first job. (10)
16 They fight to restore Rosamond’s section. (7)
17 Matrix transform vanishes when v → 0. (7)
19 Circuit complexity, typically, sounds like a religious habit (10)
22 Father of parameterised and polynomial-space algorithms, originally. (4)
24 Two-player game about encrypted mail token. (7)
25 Free variable turns leading proof assistant around. (7)
26 Additional seconds of Keynote experiments stymie brilliant talk. (5)
27 Compute |A ∪ B| as |A| + |B| like Dracula’s former girlfriend? (9)

Down

1 Maybe 20 down is a hammer made of carbon fibre? (9,6)
2 Beethoven wrote one functor in homological algebra; maybe addition. (8)
3 English statistician is positive to a degree. (5)
4 Introduces P.I.T. problem in linearly independent sets. (8)
5 Family of degree |C|. (6)
6 Tree decompostion of Sat is near. (4,5)
7 Letters from Nerode let Erdös blank out. (6)
8 Laugh at an optimal hint solving a problem. (11,4)
15 Maybe a² + b² + c² challenge keeps Naor up. (9)
17 Optimal scheduler spent day and performed many tasks. (8)
18 Where identity is unique, altogether. (2,1,5)
20 More than 64 kilobyte Nintendo retro characters. (6)
21 Neglected flow algorithm starts confusingly. (6)
23 Threaten unruly spy with hierarchy. (5)

Annotated solution