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In mathematics, in the realm of group theory, a group is algebraically closed if any finite set of equations and inequations that "make sense" in already have a solution in . This idea will be made precise later in the article. ==Informal discussion== Suppose we wished to find an element of a group satisfying the conditions (equations and inequations): :: :: :: Then it is easy to see that this is impossible because the first two equations imply . In this case we say the set of conditions are inconsistent with . (In fact this set of conditions are inconsistent with any group whatsoever.) \ |- ! style="background: #ddffdd;"| | | |- ! style="background: #ddffdd;"| | | |} |} Now suppose is the group with the multiplication table: Then the conditions: :: :: have a solution in , namely . However the conditions: :: :: Do not have a solution in , as can easily be checked. \ ! style="background: #ddffdd;"| ! style="background: #ddffdd;"| |- ! style="background: #ddffdd;"| | | | | |- ! style="background: #ddffdd;"| | | | | |- ! style="background: #ddffdd;"| | | | | |- ! style="background: #ddffdd;"| | | | | |} |} However if we extend the group to the group with multiplication table: Then the conditions have two solutions, namely and . Thus there are three possibilities regarding such conditions: * They may be inconsistent with and have no solution in any extension of . * They may have a solution in . * They may have no solution in but nevertheless have a solution in some extension of . It is reasonable to ask whether there are any groups such that whenever a set of conditions like these have a solution at all, they have a solution in itself? The answer turns out to be "yes", and we call such groups algebraically closed groups. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「algebraically closed group」の詳細全文を読む スポンサード リンク
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