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→Декартово произведение R_1\timesR_2
R <font color = grey>::</font> R1 <font color = blue>where $\lnot\exists$</font>R2 <font color = grey>(</font>R1 <font color = grey>=</font> R2<font color = grey>)</font>
=== Декартово произведение <tex>R_1\timesR_2times R_2</tex> === R1<font color = grey>.*, </font> R2<font color = grey>.* </font> <font color = blue>from </font> R1<font color = grey>, </font> R2
