theorem
  for M being strict Abelian add-associative right_zeroed
  right_complementable vector-distributive scalar-distributive
  scalar-associative scalar-unital
   non empty ModuleStr over GF, W1,W2 being
  Subspace of M holds W1 + W2 = M iff for v being Element of M ex v1,v2 being
  Element of M st v1 in W1 & v2 in W2 & v = v1 + v2 by Lm16;
