▁circ led ▁subsets ▁of ▁L ▁is ▁invariant ▁under ▁arbitrary ▁inter sections . ▁The ▁circ led ▁h ull ''' ▁of ▁A ▁is ▁the ▁intersection ▁of ▁all ▁circ led ▁subsets ▁of ▁X ▁containing ▁A . ▁ ▁Suppose ▁that ▁X ▁and ▁Y ▁are ▁vector ▁spaces ▁over ▁a ▁non - dis crete ▁valu ation ▁field ▁K , ▁let ▁A ▁ ⊆ ▁X , ▁B ▁ ⊆ ▁Y , ▁and ▁let ▁f ▁: ▁X ▁→ ▁Y ▁be ▁a ▁linear ▁map . ▁ ▁If ▁B ▁is ▁circ led ▁ ▁or ▁radial ▁then ▁so ▁is ▁. ▁If ▁A ▁is ▁circ led ▁then ▁so ▁is ▁f ( A ) ▁but ▁if ▁A ▁is ▁radial ▁then ▁f ( A ) ▁will ▁be ▁radial ▁under ▁the ▁additional ▁condition ▁that ▁f '' ▁is ▁sur jective . ▁ ▁See ▁also ▁ ▁Dis crete ▁valu ation ▁E uclidean ▁valu ation ▁Field ▁norm ▁ ▁Notes ▁ ▁References ▁▁ ▁. ▁A ▁master pie ce ▁on ▁algebra ▁written ▁by ▁one ▁of ▁the ▁leading ▁contrib utors . ▁Chapter ▁VI ▁of ▁ ▁External ▁links ▁▁ ▁Category : Al gebra ic ▁geometry ▁Category : Field ▁theory <0x0A> </s> ▁Bry an ▁S ew ell ▁Watson ▁Jones ▁( F ebru ary ▁ 2 1 , ▁ 1 8 9 7 ▁– ▁March ▁ 6 , ▁ 1 9 8 1 ) ▁was ▁an ▁American ▁football ▁coach . ▁He ▁was ▁the ▁second ▁head ▁football ▁coach ▁at ▁Ab il ene ▁Christian ▁University ▁in ▁Ab il ene , ▁Texas ▁and ▁he ▁held ▁that ▁position ▁for ▁the ▁ 1 9 2 0 ▁season . ▁His ▁co aching ▁record