insolvable
irresoluble
unsolvable
unresolvable
unsoluble
enigma
riddle
brain-teaser
conundrum
inextricable
irresolvable
intractable
trouble-shoot
troubleshoot
knotty
approximation algorithm
uncontrollable
unmanageable
insoluble
square the circle
resolvable
solvable
unsolved
unresolved
matter
Gordian knot
solvability
pig
crack
stumblingblock
swamp
corner solution
cut the Gordian knot
unovercomeable
problemo
mean
brainteaser
inapproximable
involved
hard nut to crack
unriddleable
solving
tough nut to crack
manifold
inoppugnable
resolution
approachless
undoable
unachievable
puzzle over
stumper
dys-
unrealizable
inerrable
unattainable
three-pipe problem
overcomplicated
solution
enodation
situation
problematic
kink
conflict
curly
trickily
firefighting
vexed
hydra
brainstorm
waymaking
unsurmountability
uphill
constraint
impractical
integrativity
unsolvability
wicked problem
inscrutableness
problem
unescapable
puzzledness
job
trouble
insolubility
complex
throw a wrench in
unpuzzle
escape fire
optimization problem
deus ex machina
hurdlesome
metaproblem
insolvable
irresoluble
unsolvable
unresolvable
unsoluble
inextricable
irresolvable
intractable
knotty
uncontrollable
unmanageable
insoluble
resolvable
solvable
unsolved
unresolved
unovercomeable
mean
inapproximable
involved
unriddleable
manifold
inoppugnable
approachless
undoable
unachievable
unrealizable
inerrable
unattainable
overcomplicated
problematic
curly
vexed
waymaking
impractical
unescapable
hurdlesome
trickily
uphill
enigma
riddle
brain-teaser
conundrum
approximation algorithm
matter
Gordian knot
solvability
pig
stumblingblock
swamp
corner solution
problemo
brainteaser
hard nut to crack
solving
tough nut to crack
resolution
stumper
unsolvable
three-pipe problem
solution
enodation
situation
kink
conflict
firefighting
hydra
unsurmountability
constraint
integrativity
unsolvability
wicked problem
inscrutableness
problem
puzzledness
job
trouble
insolubility
complex
escape fire
optimization problem
deus ex machina
metaproblem
trouble-shoot
troubleshoot
square the circle
riddle
crack
cut the Gordian knot
puzzle over
brainstorm
throw a wrench in
unpuzzle
English words for 'difficult to solve; intractable (problem)'
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