Metamath Proof Explorer


Theorem 9p6e15

Description: 9 + 6 = 15. (Contributed by Mario Carneiro, 19-Apr-2015)

Ref Expression
Assertion 9p6e15 ( 9 + 6 ) = 1 5

Proof

Step Hyp Ref Expression
1 9nn0 9 ∈ ℕ0
2 5nn0 5 ∈ ℕ0
3 4nn0 4 ∈ ℕ0
4 df-6 6 = ( 5 + 1 )
5 df-5 5 = ( 4 + 1 )
6 9p5e14 ( 9 + 5 ) = 1 4
7 1 2 3 4 5 6 6p5lem ( 9 + 6 ) = 1 5