Definition of a Function. A function is a relation for which each value from the set the first components of the ordered pairs is associated with exactly one value from the set of second components of the ordered pair. Okay, that is a mouth full.
Master cylinder without booster. Single bore master cylinders: These unboosted hydraulic Master Cylinders are actuated by foot effort, via the brake pedal. The brake pressure is related to actuation force and depends on the piston bore size: the smaller the bore, the higher the pressure.
That depends upon the nature of the leak. If the leakage is in the wall of the master cylinder's reservoir, you'll need to replace the master cylinder. If it's within the ABS system, you've got a lot of work to do that I can't talk you through because I won't work on ABS.