reconsider e = id the Sorts of U1 as Element of multMagma(# (MSAAut U1),(MSAAutComp U1) #) by Th24;
take e ; :: thesis: for h being Element of multMagma(# (MSAAut U1),(MSAAutComp U1) #) holds
( h * e = h & e * h = h & ex g being Element of multMagma(# (MSAAut U1),(MSAAutComp U1) #) st
( h * g = e & g * h = e ) )
let h be Element of multMagma(# (MSAAut U1),(MSAAutComp U1) #); :: thesis: ( h * e = h & e * h = h & ex g being Element of multMagma(# (MSAAut U1),(MSAAutComp U1) #) st
( h * g = e & g * h = e ) )
consider A being Element of MSAAut U1 such that
A2: A = h ;
h * e = (id the Sorts of U1) ** A by A2, Def6
.= A by MSUALG_3:4 ;
hence h * e = h by A2; :: thesis: ( e * h = h & ex g being Element of multMagma(# (MSAAut U1),(MSAAutComp U1) #) st
( h * g = e & g * h = e ) )
e * h = A ** (id the Sorts of U1) by A2, Def6
.= A by MSUALG_3:3 ;
hence e * h = h by A2; :: thesis: ex g being Element of multMagma(# (MSAAut U1),(MSAAutComp U1) #) st
( h * g = e & g * h = e )
reconsider g = A "" as Element of multMagma(# (MSAAut U1),(MSAAutComp U1) #) by Th25;
take g ; :: thesis: ( h * g = e & g * h = e )
A3: ( A is "onto" & A is "1-1" ) by Lm3;
thus h * g = (A "") ** A by A2, Def6
.= e by A3, MSUALG_3:5 ; :: thesis: g * h = e
thus g * h = A ** (A "") by A2, Def6
.= e by A3, MSUALG_3:5 ; :: thesis: verum

let f, g, h be Element of multMagma(# (MSAAut U1),(MSAAutComp U1) #); :: thesis: (f * g) * h = f * (g * h)
reconsider A = f, B = g, C = h as Element of MSAAut U1 ;
A4: g * h = C ** B by Def6;
f * g = B ** A by Def6;
hence (f * g) * h = C ** (B ** A) by Def6
.= (C ** B) ** A by PBOOLE:140
.= f * (g * h) by A4, Def6 ;
:: thesis: verum