theorem unss (A B C: set): $ A u. B C_ C <-> A C_ C /\ B C_ C $;
Step | Hyp | Ref | Expression |
1 |
|
sstr |
A C_ A u. B -> A u. B C_ C -> A C_ C |
2 |
|
ssun1 |
A C_ A u. B |
3 |
1, 2 |
ax_mp |
A u. B C_ C -> A C_ C |
4 |
|
sstr |
B C_ A u. B -> A u. B C_ C -> B C_ C |
5 |
|
ssun2 |
B C_ A u. B |
6 |
4, 5 |
ax_mp |
A u. B C_ C -> B C_ C |
7 |
3, 6 |
iand |
A u. B C_ C -> A C_ C /\ B C_ C |
8 |
|
elun |
x e. A u. B <-> x e. A \/ x e. B |
9 |
|
ssel |
A C_ C -> x e. A -> x e. C |
10 |
9 |
anwl |
A C_ C /\ B C_ C -> x e. A -> x e. C |
11 |
|
ssel |
B C_ C -> x e. B -> x e. C |
12 |
11 |
anwr |
A C_ C /\ B C_ C -> x e. B -> x e. C |
13 |
10, 12 |
eord |
A C_ C /\ B C_ C -> x e. A \/ x e. B -> x e. C |
14 |
8, 13 |
syl5bi |
A C_ C /\ B C_ C -> x e. A u. B -> x e. C |
15 |
14 |
iald |
A C_ C /\ B C_ C -> A. x (x e. A u. B -> x e. C) |
16 |
15 |
conv subset |
A C_ C /\ B C_ C -> A u. B C_ C |
17 |
7, 16 |
ibii |
A u. B C_ C <-> A C_ C /\ B C_ C |
Axiom use
axs_prop_calc
(ax_1,
ax_2,
ax_3,
ax_mp,
itru),
axs_pred_calc
(ax_gen,
ax_4,
ax_5,
ax_6,
ax_7,
ax_10,
ax_11,
ax_12),
axs_set
(elab,
ax_8)