set G = multMagma(# REAL,addreal #);
thus
for h, g, f being Element of multMagma(# REAL,addreal #) holds (h * g) * f = h * (g * f)
GROUP_1:def 3 multMagma(# REAL,addreal #) is Group-like
reconsider e = 0 as Element of multMagma(# REAL,addreal #) by XREAL_0:def 1;
take
e
; GROUP_1:def 2 for h being Element of multMagma(# REAL,addreal #) holds
( h * e = h & e * h = h & ex g being Element of multMagma(# REAL,addreal #) st
( h * g = e & g * h = e ) )
let h be Element of multMagma(# REAL,addreal #); ( h * e = h & e * h = h & ex g being Element of multMagma(# REAL,addreal #) st
( h * g = e & g * h = e ) )
reconsider A = h as Real ;
thus h * e =
A + 0
by BINOP_2:def 9
.=
h
; ( e * h = h & ex g being Element of multMagma(# REAL,addreal #) st
( h * g = e & g * h = e ) )
thus e * h =
0 + A
by BINOP_2:def 9
.=
h
; ex g being Element of multMagma(# REAL,addreal #) st
( h * g = e & g * h = e )
reconsider g = - A as Element of multMagma(# REAL,addreal #) by XREAL_0:def 1;
take
g
; ( h * g = e & g * h = e )
thus h * g =
A + (- A)
by BINOP_2:def 9
.=
e
; g * h = e
thus g * h =
(- A) + A
by BINOP_2:def 9
.=
e
; verum