Subtraction 
Subtraction is a binary operation. It should not be confused with the negative sign.
For natural numbers the the half minus operator is used which does not go below
0.
Definition
Subtraction is defined using the negative sign as
(= ( a b) (+ a (n b))) /edit/peano_new/arithmetic/common/negative.gh/dfminus.
Properties
Fraction Examples

(= ( (2) (/ (1) (3))) (/ (5) (3))) /edit/peano_new/arithmetic/common/calculations/decimal.gh/subtractFractions1

(= ( (/ (+ (10) (7)) (+ (* (2) (10)) (3))) (/ (7) (+ (10) (8)))) (/ (+ (* (10) (10)) (+ (* (4) (10)) (5))) (+ (* (4) (* (10) (10))) (+ (10) (4))))) /edit/peano_new/arithmetic/common/calculations/decimal.gh/subtractFractions2
Arithmetic Overview