| Step | Hyp | Ref | Expression | 
						
							| 1 |  | eqid | ⊢ ran  ( 𝑥  ∈  𝐵 ,  𝑦  ∈  𝐷  ↦  ( 𝑥  ×  𝑦 ) )  =  ran  ( 𝑥  ∈  𝐵 ,  𝑦  ∈  𝐷  ↦  ( 𝑥  ×  𝑦 ) ) | 
						
							| 2 | 1 | txbasex | ⊢ ( ( 𝐵  ∈  𝑉  ∧  𝐷  ∈  𝑊 )  →  ran  ( 𝑥  ∈  𝐵 ,  𝑦  ∈  𝐷  ↦  ( 𝑥  ×  𝑦 ) )  ∈  V ) | 
						
							| 3 |  | resmpo | ⊢ ( ( 𝐴  ⊆  𝐵  ∧  𝐶  ⊆  𝐷 )  →  ( ( 𝑥  ∈  𝐵 ,  𝑦  ∈  𝐷  ↦  ( 𝑥  ×  𝑦 ) )  ↾  ( 𝐴  ×  𝐶 ) )  =  ( 𝑥  ∈  𝐴 ,  𝑦  ∈  𝐶  ↦  ( 𝑥  ×  𝑦 ) ) ) | 
						
							| 4 |  | resss | ⊢ ( ( 𝑥  ∈  𝐵 ,  𝑦  ∈  𝐷  ↦  ( 𝑥  ×  𝑦 ) )  ↾  ( 𝐴  ×  𝐶 ) )  ⊆  ( 𝑥  ∈  𝐵 ,  𝑦  ∈  𝐷  ↦  ( 𝑥  ×  𝑦 ) ) | 
						
							| 5 | 3 4 | eqsstrrdi | ⊢ ( ( 𝐴  ⊆  𝐵  ∧  𝐶  ⊆  𝐷 )  →  ( 𝑥  ∈  𝐴 ,  𝑦  ∈  𝐶  ↦  ( 𝑥  ×  𝑦 ) )  ⊆  ( 𝑥  ∈  𝐵 ,  𝑦  ∈  𝐷  ↦  ( 𝑥  ×  𝑦 ) ) ) | 
						
							| 6 | 5 | adantl | ⊢ ( ( ( 𝐵  ∈  𝑉  ∧  𝐷  ∈  𝑊 )  ∧  ( 𝐴  ⊆  𝐵  ∧  𝐶  ⊆  𝐷 ) )  →  ( 𝑥  ∈  𝐴 ,  𝑦  ∈  𝐶  ↦  ( 𝑥  ×  𝑦 ) )  ⊆  ( 𝑥  ∈  𝐵 ,  𝑦  ∈  𝐷  ↦  ( 𝑥  ×  𝑦 ) ) ) | 
						
							| 7 |  | rnss | ⊢ ( ( 𝑥  ∈  𝐴 ,  𝑦  ∈  𝐶  ↦  ( 𝑥  ×  𝑦 ) )  ⊆  ( 𝑥  ∈  𝐵 ,  𝑦  ∈  𝐷  ↦  ( 𝑥  ×  𝑦 ) )  →  ran  ( 𝑥  ∈  𝐴 ,  𝑦  ∈  𝐶  ↦  ( 𝑥  ×  𝑦 ) )  ⊆  ran  ( 𝑥  ∈  𝐵 ,  𝑦  ∈  𝐷  ↦  ( 𝑥  ×  𝑦 ) ) ) | 
						
							| 8 | 6 7 | syl | ⊢ ( ( ( 𝐵  ∈  𝑉  ∧  𝐷  ∈  𝑊 )  ∧  ( 𝐴  ⊆  𝐵  ∧  𝐶  ⊆  𝐷 ) )  →  ran  ( 𝑥  ∈  𝐴 ,  𝑦  ∈  𝐶  ↦  ( 𝑥  ×  𝑦 ) )  ⊆  ran  ( 𝑥  ∈  𝐵 ,  𝑦  ∈  𝐷  ↦  ( 𝑥  ×  𝑦 ) ) ) | 
						
							| 9 |  | tgss | ⊢ ( ( ran  ( 𝑥  ∈  𝐵 ,  𝑦  ∈  𝐷  ↦  ( 𝑥  ×  𝑦 ) )  ∈  V  ∧  ran  ( 𝑥  ∈  𝐴 ,  𝑦  ∈  𝐶  ↦  ( 𝑥  ×  𝑦 ) )  ⊆  ran  ( 𝑥  ∈  𝐵 ,  𝑦  ∈  𝐷  ↦  ( 𝑥  ×  𝑦 ) ) )  →  ( topGen ‘ ran  ( 𝑥  ∈  𝐴 ,  𝑦  ∈  𝐶  ↦  ( 𝑥  ×  𝑦 ) ) )  ⊆  ( topGen ‘ ran  ( 𝑥  ∈  𝐵 ,  𝑦  ∈  𝐷  ↦  ( 𝑥  ×  𝑦 ) ) ) ) | 
						
							| 10 | 2 8 9 | syl2an2r | ⊢ ( ( ( 𝐵  ∈  𝑉  ∧  𝐷  ∈  𝑊 )  ∧  ( 𝐴  ⊆  𝐵  ∧  𝐶  ⊆  𝐷 ) )  →  ( topGen ‘ ran  ( 𝑥  ∈  𝐴 ,  𝑦  ∈  𝐶  ↦  ( 𝑥  ×  𝑦 ) ) )  ⊆  ( topGen ‘ ran  ( 𝑥  ∈  𝐵 ,  𝑦  ∈  𝐷  ↦  ( 𝑥  ×  𝑦 ) ) ) ) | 
						
							| 11 |  | ssexg | ⊢ ( ( 𝐴  ⊆  𝐵  ∧  𝐵  ∈  𝑉 )  →  𝐴  ∈  V ) | 
						
							| 12 |  | ssexg | ⊢ ( ( 𝐶  ⊆  𝐷  ∧  𝐷  ∈  𝑊 )  →  𝐶  ∈  V ) | 
						
							| 13 |  | eqid | ⊢ ran  ( 𝑥  ∈  𝐴 ,  𝑦  ∈  𝐶  ↦  ( 𝑥  ×  𝑦 ) )  =  ran  ( 𝑥  ∈  𝐴 ,  𝑦  ∈  𝐶  ↦  ( 𝑥  ×  𝑦 ) ) | 
						
							| 14 | 13 | txval | ⊢ ( ( 𝐴  ∈  V  ∧  𝐶  ∈  V )  →  ( 𝐴  ×t  𝐶 )  =  ( topGen ‘ ran  ( 𝑥  ∈  𝐴 ,  𝑦  ∈  𝐶  ↦  ( 𝑥  ×  𝑦 ) ) ) ) | 
						
							| 15 | 11 12 14 | syl2an | ⊢ ( ( ( 𝐴  ⊆  𝐵  ∧  𝐵  ∈  𝑉 )  ∧  ( 𝐶  ⊆  𝐷  ∧  𝐷  ∈  𝑊 ) )  →  ( 𝐴  ×t  𝐶 )  =  ( topGen ‘ ran  ( 𝑥  ∈  𝐴 ,  𝑦  ∈  𝐶  ↦  ( 𝑥  ×  𝑦 ) ) ) ) | 
						
							| 16 | 15 | an4s | ⊢ ( ( ( 𝐴  ⊆  𝐵  ∧  𝐶  ⊆  𝐷 )  ∧  ( 𝐵  ∈  𝑉  ∧  𝐷  ∈  𝑊 ) )  →  ( 𝐴  ×t  𝐶 )  =  ( topGen ‘ ran  ( 𝑥  ∈  𝐴 ,  𝑦  ∈  𝐶  ↦  ( 𝑥  ×  𝑦 ) ) ) ) | 
						
							| 17 | 16 | ancoms | ⊢ ( ( ( 𝐵  ∈  𝑉  ∧  𝐷  ∈  𝑊 )  ∧  ( 𝐴  ⊆  𝐵  ∧  𝐶  ⊆  𝐷 ) )  →  ( 𝐴  ×t  𝐶 )  =  ( topGen ‘ ran  ( 𝑥  ∈  𝐴 ,  𝑦  ∈  𝐶  ↦  ( 𝑥  ×  𝑦 ) ) ) ) | 
						
							| 18 | 1 | txval | ⊢ ( ( 𝐵  ∈  𝑉  ∧  𝐷  ∈  𝑊 )  →  ( 𝐵  ×t  𝐷 )  =  ( topGen ‘ ran  ( 𝑥  ∈  𝐵 ,  𝑦  ∈  𝐷  ↦  ( 𝑥  ×  𝑦 ) ) ) ) | 
						
							| 19 | 18 | adantr | ⊢ ( ( ( 𝐵  ∈  𝑉  ∧  𝐷  ∈  𝑊 )  ∧  ( 𝐴  ⊆  𝐵  ∧  𝐶  ⊆  𝐷 ) )  →  ( 𝐵  ×t  𝐷 )  =  ( topGen ‘ ran  ( 𝑥  ∈  𝐵 ,  𝑦  ∈  𝐷  ↦  ( 𝑥  ×  𝑦 ) ) ) ) | 
						
							| 20 | 10 17 19 | 3sstr4d | ⊢ ( ( ( 𝐵  ∈  𝑉  ∧  𝐷  ∈  𝑊 )  ∧  ( 𝐴  ⊆  𝐵  ∧  𝐶  ⊆  𝐷 ) )  →  ( 𝐴  ×t  𝐶 )  ⊆  ( 𝐵  ×t  𝐷 ) ) |