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Theorem mndid 15735
Description: A monoid has a two-sided identity element. (Contributed by NM, 16-Aug-2011.)
Hypotheses
Ref Expression
mndlem1.b  |-  B  =  ( Base `  G
)
mndlem1.p  |-  .+  =  ( +g  `  G )
Assertion
Ref Expression
mndid  |-  ( G  e.  Mnd  ->  E. u  e.  B  A. x  e.  B  ( (
u  .+  x )  =  x  /\  (
x  .+  u )  =  x ) )
Distinct variable groups:    x, u, B    u, G, x    u,  .+ , x

Proof of Theorem mndid
Dummy variables  y 
z are mutually distinct and distinct from all other variables.
StepHypRef Expression
1 mndlem1.b . . 3  |-  B  =  ( Base `  G
)
2 mndlem1.p . . 3  |-  .+  =  ( +g  `  G )
31, 2ismnd 15730 . 2  |-  ( G  e.  Mnd  <->  ( A. x  e.  B  A. y  e.  B  A. z  e.  B  (
( x  .+  y
)  e.  B  /\  ( ( x  .+  y )  .+  z
)  =  ( x 
.+  ( y  .+  z ) ) )  /\  E. u  e.  B  A. x  e.  B  ( ( u 
.+  x )  =  x  /\  ( x 
.+  u )  =  x ) ) )
43simprbi 464 1  |-  ( G  e.  Mnd  ->  E. u  e.  B  A. x  e.  B  ( (
u  .+  x )  =  x  /\  (
x  .+  u )  =  x ) )
Colors of variables: wff setvar class
Syntax hints:    -> wi 4    /\ wa 369    = wceq 1379    e. wcel 1767   A.wral 2814   E.wrex 2815   ` cfv 5586  (class class class)co 6282   Basecbs 14486   +g cplusg 14551   Mndcmnd 15722
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1601  ax-4 1612  ax-5 1680  ax-6 1719  ax-7 1739  ax-8 1769  ax-9 1771  ax-10 1786  ax-11 1791  ax-12 1803  ax-13 1968  ax-ext 2445  ax-nul 4576  ax-pow 4625
This theorem depends on definitions:  df-bi 185  df-or 370  df-an 371  df-3an 975  df-tru 1382  df-ex 1597  df-nf 1600  df-sb 1712  df-eu 2279  df-mo 2280  df-clab 2453  df-cleq 2459  df-clel 2462  df-nfc 2617  df-ne 2664  df-ral 2819  df-rex 2820  df-rab 2823  df-v 3115  df-sbc 3332  df-dif 3479  df-un 3481  df-in 3483  df-ss 3490  df-nul 3786  df-if 3940  df-sn 4028  df-pr 4030  df-op 4034  df-uni 4246  df-br 4448  df-iota 5549  df-fv 5594  df-ov 6285  df-mnd 15728
This theorem is referenced by:  mndideu  15736  mndidcl  15752  mndlrid  15753  prds0g  15768
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