| Step | Hyp | Ref | Expression | 
						
							| 1 |  | rngsubdi.b |  |-  B = ( Base ` R ) | 
						
							| 2 |  | rngsubdi.t |  |-  .x. = ( .r ` R ) | 
						
							| 3 |  | rngsubdi.m |  |-  .- = ( -g ` R ) | 
						
							| 4 |  | rngsubdi.r |  |-  ( ph -> R e. Rng ) | 
						
							| 5 |  | rngsubdi.x |  |-  ( ph -> X e. B ) | 
						
							| 6 |  | rngsubdi.y |  |-  ( ph -> Y e. B ) | 
						
							| 7 |  | rngsubdi.z |  |-  ( ph -> Z e. B ) | 
						
							| 8 |  | eqid |  |-  ( invg ` R ) = ( invg ` R ) | 
						
							| 9 |  | rnggrp |  |-  ( R e. Rng -> R e. Grp ) | 
						
							| 10 | 4 9 | syl |  |-  ( ph -> R e. Grp ) | 
						
							| 11 | 1 8 10 6 | grpinvcld |  |-  ( ph -> ( ( invg ` R ) ` Y ) e. B ) | 
						
							| 12 |  | eqid |  |-  ( +g ` R ) = ( +g ` R ) | 
						
							| 13 | 1 12 2 | rngdir |  |-  ( ( R e. Rng /\ ( X e. B /\ ( ( invg ` R ) ` Y ) e. B /\ Z e. B ) ) -> ( ( X ( +g ` R ) ( ( invg ` R ) ` Y ) ) .x. Z ) = ( ( X .x. Z ) ( +g ` R ) ( ( ( invg ` R ) ` Y ) .x. Z ) ) ) | 
						
							| 14 | 4 5 11 7 13 | syl13anc |  |-  ( ph -> ( ( X ( +g ` R ) ( ( invg ` R ) ` Y ) ) .x. Z ) = ( ( X .x. Z ) ( +g ` R ) ( ( ( invg ` R ) ` Y ) .x. Z ) ) ) | 
						
							| 15 | 1 2 8 4 6 7 | rngmneg1 |  |-  ( ph -> ( ( ( invg ` R ) ` Y ) .x. Z ) = ( ( invg ` R ) ` ( Y .x. Z ) ) ) | 
						
							| 16 | 15 | oveq2d |  |-  ( ph -> ( ( X .x. Z ) ( +g ` R ) ( ( ( invg ` R ) ` Y ) .x. Z ) ) = ( ( X .x. Z ) ( +g ` R ) ( ( invg ` R ) ` ( Y .x. Z ) ) ) ) | 
						
							| 17 | 14 16 | eqtrd |  |-  ( ph -> ( ( X ( +g ` R ) ( ( invg ` R ) ` Y ) ) .x. Z ) = ( ( X .x. Z ) ( +g ` R ) ( ( invg ` R ) ` ( Y .x. Z ) ) ) ) | 
						
							| 18 | 1 12 8 3 | grpsubval |  |-  ( ( X e. B /\ Y e. B ) -> ( X .- Y ) = ( X ( +g ` R ) ( ( invg ` R ) ` Y ) ) ) | 
						
							| 19 | 5 6 18 | syl2anc |  |-  ( ph -> ( X .- Y ) = ( X ( +g ` R ) ( ( invg ` R ) ` Y ) ) ) | 
						
							| 20 | 19 | oveq1d |  |-  ( ph -> ( ( X .- Y ) .x. Z ) = ( ( X ( +g ` R ) ( ( invg ` R ) ` Y ) ) .x. Z ) ) | 
						
							| 21 | 1 2 | rngcl |  |-  ( ( R e. Rng /\ X e. B /\ Z e. B ) -> ( X .x. Z ) e. B ) | 
						
							| 22 | 4 5 7 21 | syl3anc |  |-  ( ph -> ( X .x. Z ) e. B ) | 
						
							| 23 | 1 2 | rngcl |  |-  ( ( R e. Rng /\ Y e. B /\ Z e. B ) -> ( Y .x. Z ) e. B ) | 
						
							| 24 | 4 6 7 23 | syl3anc |  |-  ( ph -> ( Y .x. Z ) e. B ) | 
						
							| 25 | 1 12 8 3 | grpsubval |  |-  ( ( ( X .x. Z ) e. B /\ ( Y .x. Z ) e. B ) -> ( ( X .x. Z ) .- ( Y .x. Z ) ) = ( ( X .x. Z ) ( +g ` R ) ( ( invg ` R ) ` ( Y .x. Z ) ) ) ) | 
						
							| 26 | 22 24 25 | syl2anc |  |-  ( ph -> ( ( X .x. Z ) .- ( Y .x. Z ) ) = ( ( X .x. Z ) ( +g ` R ) ( ( invg ` R ) ` ( Y .x. Z ) ) ) ) | 
						
							| 27 | 17 20 26 | 3eqtr4d |  |-  ( ph -> ( ( X .- Y ) .x. Z ) = ( ( X .x. Z ) .- ( Y .x. Z ) ) ) |