Definition df-djud 6988

Description: The "domain-disjoint-union" of two relations: if 𝑅 ⊆ (𝐴 × 𝑋) and 𝑆 ⊆ (𝐵 × 𝑋) are two binary relations, then (𝑅 ⊔_d 𝑆) is the binary relation from (𝐴 ⊔ 𝐵) to 𝑋 having the universal property of disjoint unions (see updjud 6967 in the case of functions).

Remark: the restrictions to dom 𝑅 (resp. dom 𝑆) are not necessary since extra stuff would be thrown away in the post-composition with 𝑅 (resp. 𝑆), as in df-case 6969, but they are explicitly written for clarity. (Contributed by MC and BJ, 10-Jul-2022.)

Assertion

Ref	Expression
df-djud	⊢ (𝑅 ⊔d 𝑆) = ((𝑅 ∘ ◡(inl ↾ dom 𝑅)) ∪ (𝑆 ∘ ◡(inr ↾ dom 𝑆)))

Detailed syntax breakdown of Definition df-djud

Step	Hyp	Ref	Expression
1		cR	. . 3 class 𝑅
2		cS	. . 3 class 𝑆
3	1, 2	cdjud 6987	. 2 class (𝑅 ⊔d 𝑆)
4		cinl 6930	. . . . . 6 class inl
5	1	cdm 4539	. . . . . 6 class dom 𝑅
6	4, 5	cres 4541	. . . . 5 class (inl ↾ dom 𝑅)
7	6	ccnv 4538	. . . 4 class ◡(inl ↾ dom 𝑅)
8	1, 7	ccom 4543	. . 3 class (𝑅 ∘ ◡(inl ↾ dom 𝑅))
9		cinr 6931	. . . . . 6 class inr
10	2	cdm 4539	. . . . . 6 class dom 𝑆
11	9, 10	cres 4541	. . . . 5 class (inr ↾ dom 𝑆)
12	11	ccnv 4538	. . . 4 class ◡(inr ↾ dom 𝑆)
13	2, 12	ccom 4543	. . 3 class (𝑆 ∘ ◡(inr ↾ dom 𝑆))
14	8, 13	cun 3069	. 2 class ((𝑅 ∘ ◡(inl ↾ dom 𝑅)) ∪ (𝑆 ∘ ◡(inr ↾ dom 𝑆)))
15	3, 14	wceq 1331	1 wff (𝑅 ⊔d 𝑆) = ((𝑅 ∘ ◡(inl ↾ dom 𝑅)) ∪ (𝑆 ∘ ◡(inr ↾ dom 𝑆)))

This definition is referenced by:  djufun  6989  djudm  6990  djuinj  6991