| Step | Hyp | Ref | Expression | 
						
							| 1 |  | df-tpos | ⊢ tpos  𝐹  =  ( 𝐹  ∘  ( 𝑥  ∈  ( ◡ dom  𝐹  ∪  { ∅ } )  ↦  ∪  ◡ { 𝑥 } ) ) | 
						
							| 2 |  | cossxp | ⊢ ( 𝐹  ∘  ( 𝑥  ∈  ( ◡ dom  𝐹  ∪  { ∅ } )  ↦  ∪  ◡ { 𝑥 } ) )  ⊆  ( dom  ( 𝑥  ∈  ( ◡ dom  𝐹  ∪  { ∅ } )  ↦  ∪  ◡ { 𝑥 } )  ×  ran  𝐹 ) | 
						
							| 3 | 1 2 | eqsstri | ⊢ tpos  𝐹  ⊆  ( dom  ( 𝑥  ∈  ( ◡ dom  𝐹  ∪  { ∅ } )  ↦  ∪  ◡ { 𝑥 } )  ×  ran  𝐹 ) | 
						
							| 4 |  | eqid | ⊢ ( 𝑥  ∈  ( ◡ dom  𝐹  ∪  { ∅ } )  ↦  ∪  ◡ { 𝑥 } )  =  ( 𝑥  ∈  ( ◡ dom  𝐹  ∪  { ∅ } )  ↦  ∪  ◡ { 𝑥 } ) | 
						
							| 5 | 4 | dmmptss | ⊢ dom  ( 𝑥  ∈  ( ◡ dom  𝐹  ∪  { ∅ } )  ↦  ∪  ◡ { 𝑥 } )  ⊆  ( ◡ dom  𝐹  ∪  { ∅ } ) | 
						
							| 6 |  | xpss1 | ⊢ ( dom  ( 𝑥  ∈  ( ◡ dom  𝐹  ∪  { ∅ } )  ↦  ∪  ◡ { 𝑥 } )  ⊆  ( ◡ dom  𝐹  ∪  { ∅ } )  →  ( dom  ( 𝑥  ∈  ( ◡ dom  𝐹  ∪  { ∅ } )  ↦  ∪  ◡ { 𝑥 } )  ×  ran  𝐹 )  ⊆  ( ( ◡ dom  𝐹  ∪  { ∅ } )  ×  ran  𝐹 ) ) | 
						
							| 7 | 5 6 | ax-mp | ⊢ ( dom  ( 𝑥  ∈  ( ◡ dom  𝐹  ∪  { ∅ } )  ↦  ∪  ◡ { 𝑥 } )  ×  ran  𝐹 )  ⊆  ( ( ◡ dom  𝐹  ∪  { ∅ } )  ×  ran  𝐹 ) | 
						
							| 8 | 3 7 | sstri | ⊢ tpos  𝐹  ⊆  ( ( ◡ dom  𝐹  ∪  { ∅ } )  ×  ran  𝐹 ) |