| Step | Hyp | Ref | Expression | 
						
							| 1 |  | stle.1 |  |-  A e. CH | 
						
							| 2 |  | stle.2 |  |-  B e. CH | 
						
							| 3 |  | stm1add3.3 |  |-  C e. CH | 
						
							| 4 | 1 2 | chincli |  |-  ( A i^i B ) e. CH | 
						
							| 5 | 4 3 | stm1i |  |-  ( S e. States -> ( ( S ` ( ( A i^i B ) i^i C ) ) = 1 -> ( S ` ( A i^i B ) ) = 1 ) ) | 
						
							| 6 | 1 2 | stm1addi |  |-  ( S e. States -> ( ( S ` ( A i^i B ) ) = 1 -> ( ( S ` A ) + ( S ` B ) ) = 2 ) ) | 
						
							| 7 | 5 6 | syld |  |-  ( S e. States -> ( ( S ` ( ( A i^i B ) i^i C ) ) = 1 -> ( ( S ` A ) + ( S ` B ) ) = 2 ) ) | 
						
							| 8 | 4 3 | stm1ri |  |-  ( S e. States -> ( ( S ` ( ( A i^i B ) i^i C ) ) = 1 -> ( S ` C ) = 1 ) ) | 
						
							| 9 | 7 8 | jcad |  |-  ( S e. States -> ( ( S ` ( ( A i^i B ) i^i C ) ) = 1 -> ( ( ( S ` A ) + ( S ` B ) ) = 2 /\ ( S ` C ) = 1 ) ) ) | 
						
							| 10 |  | oveq12 |  |-  ( ( ( ( S ` A ) + ( S ` B ) ) = 2 /\ ( S ` C ) = 1 ) -> ( ( ( S ` A ) + ( S ` B ) ) + ( S ` C ) ) = ( 2 + 1 ) ) | 
						
							| 11 |  | df-3 |  |-  3 = ( 2 + 1 ) | 
						
							| 12 | 10 11 | eqtr4di |  |-  ( ( ( ( S ` A ) + ( S ` B ) ) = 2 /\ ( S ` C ) = 1 ) -> ( ( ( S ` A ) + ( S ` B ) ) + ( S ` C ) ) = 3 ) | 
						
							| 13 | 9 12 | syl6 |  |-  ( S e. States -> ( ( S ` ( ( A i^i B ) i^i C ) ) = 1 -> ( ( ( S ` A ) + ( S ` B ) ) + ( S ` C ) ) = 3 ) ) |