文摘
Let class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0012365X16000200&_mathId=si2.gif&_user=111111111&_pii=S0012365X16000200&_rdoc=1&_issn=0012365X&md5=8de5f847d72d7a30f4a2776327ebe4ee" title="Click to view the MathML source">Eclass="mathContainer hidden">class="mathCode"> (respectively; class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0012365X16000200&_mathId=si3.gif&_user=111111111&_pii=S0012365X16000200&_rdoc=1&_issn=0012365X&md5=5ca220a01bfe514f31ad3f8d0f57fdab" title="Click to view the MathML source">Tclass="mathContainer hidden">class="mathCode">, class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0012365X16000200&_mathId=si4.gif&_user=111111111&_pii=S0012365X16000200&_rdoc=1&_issn=0012365X&md5=d856cf96beccc3734e24ecd736e9258c" title="Click to view the MathML source">Sclass="mathContainer hidden">class="mathCode">) denote the set of all lines which are external (respectively; tangent, secant) to an irreducible conic in class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0012365X16000200&_mathId=si1.gif&_user=111111111&_pii=S0012365X16000200&_rdoc=1&_issn=0012365X&md5=30258dcca7c9287c400dd56124421ac7" title="Click to view the MathML source">PG(2,q)class="mathContainer hidden">class="mathCode">. We give a brief survey of the known results regarding the minimum size class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0012365X16000200&_mathId=si6.gif&_user=111111111&_pii=S0012365X16000200&_rdoc=1&_issn=0012365X&md5=ac23928cacd508fe231f9b471c2eeaf0" title="Click to view the MathML source">Lclass="mathContainer hidden">class="mathCode">-blocking sets of class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0012365X16000200&_mathId=si1.gif&_user=111111111&_pii=S0012365X16000200&_rdoc=1&_issn=0012365X&md5=30258dcca7c9287c400dd56124421ac7" title="Click to view the MathML source">PG(2,q)class="mathContainer hidden">class="mathCode"> for class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0012365X16000200&_mathId=si8.gif&_user=111111111&_pii=S0012365X16000200&_rdoc=1&_issn=0012365X&md5=1f59de0f7754e852d4e3cb2ef3c11230" title="Click to view the MathML source">L∈{E,S,T∪E,T∪S}class="mathContainer hidden">class="mathCode"> and study the other two cases when class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0012365X16000200&_mathId=si9.gif&_user=111111111&_pii=S0012365X16000200&_rdoc=1&_issn=0012365X&md5=17e2d79a629cc92a45698ba7549ccabb" title="Click to view the MathML source">L=Tclass="mathContainer hidden">class="mathCode">, class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0012365X16000200&_mathId=si10.gif&_user=111111111&_pii=S0012365X16000200&_rdoc=1&_issn=0012365X&md5=8d28c057a7cc3d5ad0576de0c1b39e7c" title="Click to view the MathML source">E∪Sclass="mathContainer hidden">class="mathCode">.