Theorem n0i 3368

Description: If a set has elements, it is not empty. A set with elements is also inhabited, see elex2 2702. (Contributed by NM, 31-Dec-1993.)

Assertion

Ref	Expression
n0i	|- ( B e. A -> -. A = (/) )

Proof of Theorem n0i

Step	Hyp	Ref	Expression
1		noel 3367	. . 3 |- -. B e. (/)
2		eleq2 2203	. . 3 |- ( A = (/) -> ( B e. A <-> B e. (/) ) )
3	1, 2	mtbiri 664	. 2 |- ( A = (/) -> -. B e. A )
4	3	con2i 616	1 |- ( B e. A -> -. A = (/) )

Syntax hints:   -. wn 3   -> wi 4   = wceq 1331   e. wcel 1480   (/)c0 3363

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-in1 603  ax-in2 604  ax-io 698  ax-5 1423  ax-7 1424  ax-gen 1425  ax-ie1 1469  ax-ie2 1470  ax-8 1482  ax-10 1483  ax-11 1484  ax-i12 1485  ax-bndl 1486  ax-4 1487  ax-17 1506  ax-i9 1510  ax-ial 1514  ax-i5r 1515  ax-ext 2121

This theorem depends on definitions:  df-bi 116  df-tru 1334  df-nf 1437  df-sb 1736  df-clab 2126  df-cleq 2132  df-clel 2135  df-nfc 2270  df-v 2688  df-dif 3073  df-nul 3364

This theorem is referenced by:  ne0i  3369  n0ii  3371  unidif0  4091  iin0r  4093  nnm00  6425  dif1enen  6774  enq0tr  7242