Metamath Proof Explorer


Theorem absori

Description: The absolute value of a real number is either that number or its negative. (Contributed by NM, 30-Sep-1999)

Ref Expression
Hypothesis sqrtthi.1 A
Assertion absori A=AA=A

Proof

Step Hyp Ref Expression
1 sqrtthi.1 A
2 absor AA=AA=A
3 1 2 ax-mp A=AA=A