Changes

==Casual introduction==

==Casual introduction==

Consider the situation represented by the following venn diagram.

Consider the situation represented by the venn diagram in Figure 1.

<center><pre>

<center><pre>

The area of the rectangle represents a universe of discourse, <math>X.\!</math>  This might be a population of individuals having various additional properties or it might be a collection of locations that various individuals occupy.  The area of the "circle" represents the individuals that have the property <math>q\!</math> or the locations that fall within the corresponding region <math>Q.\!</math>  Four individuals, <math>h, i, j, k,\!</math> are singled out by name.  It happens that <math>i\!</math> and <math>j\!</math> currently reside in region <math>Q\!</math> while <math>h\!</math> and <math>k\!</math> do not.

The area of the rectangle represents a universe of discourse, <math>X.\!</math>  This might be a population of individuals having various additional properties or it might be a collection of locations that various individuals occupy.  The area of the "circle" represents the individuals that have the property <math>q\!</math> or the locations that fall within the corresponding region <math>Q.\!</math>  Four individuals, <math>h, i, j, k,\!</math> are singled out by name.  It happens that <math>i\!</math> and <math>j\!</math> currently reside in region <math>Q\!</math> while <math>h\!</math> and <math>k\!</math> do not.

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