Metamath Proof Explorer


Theorem untuni

Description: The union of a class is untangled iff all its members are untangled. (Contributed by Scott Fenton, 28-Feb-2011)

Ref Expression
Assertion untuni xA¬xxyAxy¬xx

Proof

Step Hyp Ref Expression
1 r19.23v yAxy¬xxyAxy¬xx
2 1 albii xyAxy¬xxxyAxy¬xx
3 ralcom4 yAxxy¬xxxyAxy¬xx
4 eluni2 xAyAxy
5 4 imbi1i xA¬xxyAxy¬xx
6 5 albii xxA¬xxxyAxy¬xx
7 2 3 6 3bitr4ri xxA¬xxyAxxy¬xx
8 df-ral xA¬xxxxA¬xx
9 df-ral xy¬xxxxy¬xx
10 9 ralbii yAxy¬xxyAxxy¬xx
11 7 8 10 3bitr4i xA¬xxyAxy¬xx