let V be RealLinearSpace; for w, y being VECTOR of V
for a, a1, a2 being Element of (DTrSpace (V,w,y)) st a # a1 = a # a2 holds
a1 = a2
let w, y be VECTOR of V; for a, a1, a2 being Element of (DTrSpace (V,w,y)) st a # a1 = a # a2 holds
a1 = a2
let a, a1, a2 be Element of (DTrSpace (V,w,y)); ( a # a1 = a # a2 implies a1 = a2 )
assume A1:
a # a1 = a # a2
; a1 = a2
reconsider u = a, u1 = a1, u2 = a2 as VECTOR of V ;
( u # u1 = a # a1 & u # u2 = a # a2 )
by Def8;
hence
a1 = a2
by A1, Th7; verum