Metamath Proof Explorer

Theorem btwncom

Description: Betweenness commutes. (Contributed by Scott Fenton, 12-Jun-2013)

Ref Expression
Assertion btwncom 
|- ( ( N e. NN /\ ( A e. ( EE ` N ) /\ B e. ( EE ` N ) /\ C e. ( EE ` N ) ) ) -> ( A Btwn <. B , C >. <-> A Btwn <. C , B >. ) )

Proof

Step Hyp Ref Expression
1 btwncomim 
 |-  ( ( N e. NN /\ ( A e. ( EE ` N ) /\ B e. ( EE ` N ) /\ C e. ( EE ` N ) ) ) -> ( A Btwn <. B , C >. -> A Btwn <. C , B >. ) )
2 3ancomb 
 |-  ( ( A e. ( EE ` N ) /\ B e. ( EE ` N ) /\ C e. ( EE ` N ) ) <-> ( A e. ( EE ` N ) /\ C e. ( EE ` N ) /\ B e. ( EE ` N ) ) )
3 btwncomim 
 |-  ( ( N e. NN /\ ( A e. ( EE ` N ) /\ C e. ( EE ` N ) /\ B e. ( EE ` N ) ) ) -> ( A Btwn <. C , B >. -> A Btwn <. B , C >. ) )
4 2 3 sylan2b 
 |-  ( ( N e. NN /\ ( A e. ( EE ` N ) /\ B e. ( EE ` N ) /\ C e. ( EE ` N ) ) ) -> ( A Btwn <. C , B >. -> A Btwn <. B , C >. ) )
5 1 4 impbid 
 |-  ( ( N e. NN /\ ( A e. ( EE ` N ) /\ B e. ( EE ` N ) /\ C e. ( EE ` N ) ) ) -> ( A Btwn <. B , C >. <-> A Btwn <. C , B >. ) )