:: deftheorem Def4 defines QClass. QUOFIELD:def 4 :
for I being non empty non degenerated multLoopStr_0
for u being Element of Q. I
for b₃ being Subset of (Q. I) holds
( b₃ = QClass. u iff for z being Element of Q. I holds
( z in b₃ iff (z `1) * (u `2) = (z `2) * (u `1) ) );