pre-image
and 
, the pre-image 
of A is
This notation does not imply that f is invertible (see invertible function). Note 
, but equality does not generally hold.
- acceptance sampling
- accessibility
- accumulation point
- accuracy
- accurate (correct) to n decimal places
- accurate (correct) to n significant figures
- Acheson, David
- Achilles paradox
- acnode
- action
- action, acts
- action limits
- active constraint
- activity networks
- activity networks
- actual infinity
- acute angle
- acyclic
- addend
- adders
- addition
- addition
- addition
- addition
- addition formulae