defpred S₁[ object ] means ex W being strict Subspace of V st
( W = $1 & dim W = n );
for X1, X2 being set st ( for x being object holds
( x in X1 iff S₁[x] ) ) & ( for x being object holds
( x in X2 iff S₁[x] ) ) holds
X1 = X2 from XBOOLE_0:sch 3();
hence for b₁, b₂ being set st ( for x being object holds
( x in b₁ iff ex W being strict Subspace of V st
( W = x & dim W = n ) ) ) & ( for x being object holds
( x in b₂ iff ex W being strict Subspace of V st
( W = x & dim W = n ) ) ) holds
b₁ = b₂ ; :: thesis: verum