Clue: Chap in key wager collapses complex mathematical construction (10,3)
Answer: MANDELBROT SET
Explanation: Definition: complex mathematical construction
MAN + ROTS in DEL (computer key) BET. By coincidence (and for reasons too complicated to explain) I was thinking about the Mandelbrot set while lying in bed last night, and perhaps as a result this was one of my first entries. It's a geometrical object of astonishing complexity and great beauty (and complex in another way, as its definition uses the so-called complex numbers)