:: deftheorem Def1 defines ker RANKNULL:def 1 :
for F being Ring
for V, W being VectSp of F
for T being linear-transformation of V,W
for b₅ being strict Subspace of V holds
( b₅ = ker T iff [#] b₅ = { u where u is Element of V : T . u = 0. W } );