| |||
challenge (MichaelBurov); brain teaser (син. brain-twister; puzzle, problem, riddle, conundrum, poser Taras) | |||
weighty problem | |||
difficult nut to crack (Violetta Gun.); insidious problem (Wolverin) | |||
intractable problem | |||
formidable task (ssn) |
трудноразрешимая задача: 1 phrase in 1 subject |
Mathematics | 1 |