Metamath Proof Explorer


Theorem fixun

Description: The fixpoint operator distributes over union. (Contributed by Scott Fenton, 16-Apr-2012)

Ref Expression
Assertion fixun 𝖥𝗂𝗑 A B = 𝖥𝗂𝗑 A 𝖥𝗂𝗑 B

Proof

Step Hyp Ref Expression
1 indir A B I = A I B I
2 1 dmeqi dom A B I = dom A I B I
3 dmun dom A I B I = dom A I dom B I
4 2 3 eqtri dom A B I = dom A I dom B I
5 df-fix 𝖥𝗂𝗑 A B = dom A B I
6 df-fix 𝖥𝗂𝗑 A = dom A I
7 df-fix 𝖥𝗂𝗑 B = dom B I
8 6 7 uneq12i 𝖥𝗂𝗑 A 𝖥𝗂𝗑 B = dom A I dom B I
9 4 5 8 3eqtr4i 𝖥𝗂𝗑 A B = 𝖥𝗂𝗑 A 𝖥𝗂𝗑 B