A double downward-pointing arrow symbol commonly used to indicate strong downward implications or descent in mathematical proofs and diagrams.
Examples
Downward implication in logical reasoning
P \dArr Q \text{ indicates P implies Q (vertical notation)}
Showing sequential steps in a proof
x > 0 \dArr x^2 > 0 \dArr \sqrt{x^2} > 0
Indicating decrease or descent in a sequence
a_n = n^2 \dArr a_{n-1} = (n-1)^2 \text{ for } n > 1