let V be ComplexLinearSpace; :: thesis: for V1 being Subset of V st V1 is linearly-closed holds
for v, u being VECTOR of V st v in V1 & u in V1 holds
v - u in V1
let V1 be Subset of V; :: thesis: ( V1 is linearly-closed implies for v, u being VECTOR of V st v in V1 & u in V1 holds
v - u in V1 )
assume A1: V1 is linearly-closed ; :: thesis: for v, u being VECTOR of V st v in V1 & u in V1 holds
v - u in V1
let v, u be VECTOR of V; :: thesis: ( v in V1 & u in V1 implies v - u in V1 )
assume that
A2: v in V1 and
A3: u in V1 ; :: thesis: v - u in V1
- u in V1 by A1, A3, Th21;
hence v - u in V1 by A1, A2; :: thesis: verum