set cR = the carrier of R;
set ccs = NonZero R;
A1:
not 1_ R in {(0. R)}
by TARSKI:def 1;
reconsider ccs = NonZero R as non empty set ;
set mcs = the multF of R || ccs;
[:ccs,ccs:] c= [:the carrier of R,the carrier of R:]
then reconsider mcs = the multF of R || ccs as Function of [:ccs,ccs:],the carrier of R by FUNCT_2:38;
rng mcs c= ccs
proof
let y be
set ;
:: according to TARSKI:def 3 :: thesis: ( not y in rng mcs or y in ccs )
assume
y in rng mcs
;
:: thesis: y in ccs
then consider x being
set such that A4:
x in dom mcs
and A5:
y = mcs . x
by FUNCT_1:def 5;
A6:
dom mcs = [:ccs,ccs:]
by FUNCT_2:def 1;
then consider a,
b being
set such that A7:
(
a in ccs &
b in ccs )
and A8:
x = [a,b]
by A4, ZFMISC_1:def 2;
reconsider a =
a,
b =
b as
Element of the
carrier of
R by A7;
( not
a in {(0. R)} & not
b in {(0. R)} )
by A7, XBOOLE_0:def 5;
then
(
a <> 0. R &
b <> 0. R )
by TARSKI:def 1;
then
a * b <> 0. R
by VECTSP_2:47;
then A9:
not
a * b in {(0. R)}
by TARSKI:def 1;
mcs . x = a * b
by A4, A6, A8, FUNCT_1:72;
hence
y in ccs
by A5, A9, XBOOLE_0:def 5;
:: thesis: verum
end;
then reconsider mcs = mcs as BinOp of ccs by FUNCT_2:8;
reconsider cs = multMagma(# ccs,mcs #) as non empty multMagma ;
set ccs1 = the carrier of cs;
A12:
cs is associative
cs is Group-like
hence
ex b1 being strict Group st
( the carrier of b1 = NonZero R & the multF of b1 = the multF of R || the carrier of b1 )
by A12; :: thesis: verum