Orderings of the 46 ToC topics marked as 'essential' in the ToC survey
Topics: ordered on percent 'essential'	%	Topics: ordered on average response	(1<= x <= 3)
Regular_expressions[SQ007]	98.55	Regular_expressions[SQ007]	2.99
Deterministic Finite Automata (DFA)[SQ001]	95.71	The Turing Machine (basics)[SQ024]	2.94
The Turing Machine (basics)[SQ024]	94.37	Deterministic Finite Automata (DFA)[SQ001]	2.94
Context-free Grammars (definition, ambiguity, simplification, derivations)[SQ013]	94.20	Context-free Grammars (definition, ambiguity, simplification, derivations)[SQ013]	2.94
Non-Deterministic Finite Automata (NFA, epsilon-NFA)[SQ002]	88.41	Non-Deterministic Finite Automata (NFA, epsilon-NFA)[SQ002]	2.86
Equivalences & conversion RE and automata[SQ008]	85.29	Equivalences & conversion RE and automata[SQ008]	2.84
Problems a computer cannot solve[SQ020]	85.29	Problems a computer cannot solve[SQ020]	2.81
Halting problem[SQ040]	82.81	Halting problem[SQ040]	2.80
Properties of Regular languages[SQ012]	80.30	Properties of Regular languages[SQ012]	2.77
Regular grammars (RG)[SQ009]	80.00	Examples of some undecidable problems/languages[SQ038]	2.77
Examples of some undecidable problems/languages[SQ038]	78.13	Computability and decidability[SQ030]	2.75
Church-Turing thesis[SQ023]	77.94	Church-Turing thesis[SQ023]	2.75
Computability and decidability[SQ030]	76.81	Regular grammars (RG)[SQ009]	2.74
Equivalences & conversion DFA, NFA, epsilon-NFA[SQ003]	73.85	P, NP, NP-complete, NP-hard, co-NP[SQ041]	2.72
P, NP, NP-complete, NP-hard, co-NP[SQ041]	73.53	Universal Turing Machine[SQ034]	2.69
Universal Turing Machine[SQ034]	72.06	Equivalences & conversion DFA, NFA, epsilon-NFA[SQ003]	2.68
Undecidability[SQ031]	68.57	Undecidability[SQ031]	2.67
Pumping lemma for Regular languages[SQ011]	68.18	Some well-known NP problems (e.g., TSP, SAT, Node cover)[SQ044]	2.64
Some well-known NP problems (e.g., TSP, SAT, Node cover)[SQ044]	68.18	Reductions[SQ022]	2.61
Chomsky normal form, hierarchy[SQ014]	67.16	Chomsky normal form, hierarchy[SQ014]	2.60
Reductions[SQ022]	65.15	Polynomial time reductions[SQ042]	2.60
Proving undecidability[SQ021]	62.86	Show problem to be decidable/undecidable (RE, non-RE, RE but not Rec.)[SQ039]	2.59
Polynomial time reductions[SQ042]	62.69	Pumping lemma for Regular languages[SQ011]	2.58
Show problem to be decidable/undecidable (RE, non-RE, RE but not Rec.)[SQ039]	61.90	Proving undecidability[SQ021]	2.56
Push-down Automata (PDA, deterministic and non-deterministic)[SQ015]	61.54	Push-down Automata (PDA, deterministic and non-deterministic)[SQ015]	2.55
Converting RG NFAs[SQ010]	60.61	TM acceptors[SQ025]	2.52
TM acceptors[SQ025]	57.14	Show problem to be P, NP, NP-complete, NP-hard, co-NP[SQ043]	2.48
Pumping lemma for CFLs[SQ016]	54.69	Converting RG NFAs[SQ010]	2.47
Equivalences & conversion PDA, CFG[SQ019]	51.61	Recursively Enumerable, non-RE, RE but not recursive languages[SQ033]	2.42
Show problem to be P, NP, NP-complete, NP-hard, co-NP[SQ043]	50.75	Equivalences & conversion PDA, CFG[SQ019]	2.39
State minimization[SQ004]	49.25	Non-deterministic TM[SQ029]	2.36
Closure properties of CFLs[SQ018]	49.21	Pumping lemma for CFLs[SQ016]	2.36
Recursively Enumerable, non-RE, RE but not recursive languages[SQ033]	46.38	State minimization[SQ004]	2.33
Decision properties of CFLs[SQ017]	46.03	Decision properties of CFLs[SQ017]	2.30
Non-deterministic TM[SQ029]	45.45	Closure properties of CFLs[SQ018]	2.30
Cook's theorem[SQ036]	38.71	Cook's theorem[SQ036]	2.27
Diagonalization language[SQ032]	34.38	Diagonalization language[SQ032]	2.17
Multi-tape TM[SQ028]	30.88	Post correspondence problem[SQ037]	2.12
Rice's theorem[SQ035]	30.00	PSPACE, EXPTIME, ...[SQ045]	2.10
Post correspondence problem[SQ037]	26.67	Multi-tape TM[SQ028]	2.09
PSPACE, EXPTIME, ...[SQ045]	26.23	Rice's theorem[SQ035]	2.08
Moore Machines[SQ005]	21.31	TM transducers[SQ026]	1.95
Mealy Machines[SQ006]	21.31	programming tricks' for TM (storage, tracks)[SQ027]	1.93
programming tricks' for TM (storage, tracks)[SQ027]	20.59	hot/fun topics' and their complexity classes (e.g., games)[SQ046]	1.89
TM transducers[SQ026]	17.74	Moore Machines[SQ005]	1.79
hot/fun topics' and their complexity classes (e.g., games)[SQ046]	15.87	Mealy Machines[SQ006]	1.75